KSH(1)

📦

version 93vu · 7 versions

93vu · opensuse-leap 16.0 (latest)
1.0.6 · centos-stream 9
1.0.0~beta.2 · ubuntu jammy
1.0.8 · ubuntu noble
1.0.10 · centos-stream 10, fedora 43, fedora 44
1.0.4 · debian bookworm
1.0.10 · debian trixie, ubuntu questing, ubuntu resolute, ubuntu stonking

🌸 NAME 🌸

ksh, rksh, pfksh — KornShell, a standard/restricted command and programming language

ok so real talk, this whole page is from the General Commands Manual, and it's the entire personality of KornShell. buckle up bestie, it's a long one 💖

✨ SYNOPSIS ✨

ksh [ ±abcefhikmnoprstuvxBCDP ] [ -R file ] [ ±o option ] ... [ - ] [ arg ... ]
rksh [ ±abcefhikmnoprstuvxBCD ] [ -R file ] [ ±o option ] ...  [ - ] [ arg ... ]

🦋 DESCRIPTION 🦋

ksh is a command and programming language that executes commands read from a terminal or a file. icon behavior honestly.

rksh is a restricted version of the command interpreter ksh — it's the one you use to set up login names and execution environments whose capabilities are more controlled than those of the standard shell. locked down, on purpose, no cap 🔒

rpfksh is a profile shell version of the command interpreter ksh — it's used to execute commands with the attributes specified by the user's profiles (see pfexec(1)). very "I have a permission slip" of it tbh.

peep Invocation below for what the arguments to the shell actually mean 👀

💅 Definitions.

so before we get into it, the vocabulary check, because the shell is gonna use these words a LOT:

A metacharacter is one of these characters: ;, &, (, ), |, <, >, new-line, space, tab. these are the little guys with main character energy — the shell treats them specially.
A blank is a tab or a space.
An identifier is a sequence of letters, digits, or underscores starting with a letter or underscore. Identifiers are used as components of variable names.
A vname is a sequence of one or more identifiers separated by a . and optionally preceded by a .. Vnames are used as function and variable names. (yes, dots. it's giving file path but make it variable 💫)
A word is a sequence of characters from the character set defined by the current locale, excluding non-quoted metacharacters.

A command is a sequence of characters in the syntax of the shell language. The shell reads each command and carries out the desired action either directly or by invoking separate utilities.

A built-in command is a command that is carried out by the shell itself, without creating a separate process. Some commands are built-in purely for convenience and are not documented here. Built-ins that cause side effects in the shell environment and built-ins that are found before performing a path search (see Execution below) are documented here. And for historical reasons, some of these built-ins behave differently than other built-ins and are called special built-ins. yes they have lore. we respect the lore 👑

🎀 Commands.

the basics, aka simple-command

A simple-command is a list of variable assignments (see Variable Assignments below) or a sequence of blank separated words which may be preceded by a list of variable assignments (see Environment below).

The first word specifies the name of the command to be executed. Except as specified below, the remaining words are passed as arguments to the invoked command. The command name is passed as argument 0 (see exec(2)).

The value of a simple-command is its exit status:

0-255 if it terminates normally
256+signum if it terminates abnormally

(the name of the signal corresponding to the exit status can be obtained via the -l option of the kill built-in utility — cute little decoder ring 🔍)

pipelines

A pipeline is a sequence of one or more commands separated by |. The standard output of each command but the last is connected by socketpair(2) to the standard input of the next command. Each command, except possibly the last, is run as a separate process; the shell waits for the last command to terminate.

The exit status of a pipeline is the exit status of the last command — unless the pipefail option is enabled. (rude little setting, but okay)

Each pipeline can be preceded by the reserved word ! which causes the exit status of the pipeline to become 0 if the exit status of the last command is non-zero, and 1 if the exit status of the last command is 0. it's the uno reverse card 🃏

lists

A list is a sequence of one or more pipelines separated by ;, &, |&, &&, or ||, and optionally terminated by ;, &, or |&.

precedence tea ☕ of these five symbols:

;, &, and |& have equal precedence, which is lower than that of && and ||
&& and || also have equal precedence

what they actually do:

A semicolon (;) causes sequential execution of the preceding pipeline.
An ampersand (&) causes asynchronous execution of the preceding pipeline (i.e., the shell does not wait for that pipeline to finish).
The symbol |& causes asynchronous execution of the preceding pipeline with a two-way pipe established to the parent shell; the standard input and output of the spawned pipeline can be written to and read from by the parent shell by applying the redirection operators <& and >& with arg p to commands, and by using the -p option of the built-in commands read and print described later. two-way communication, we love a dialogue 💬
The symbol && (||) causes the list following it to be executed only if the preceding pipeline returns a zero (non-zero) value.

One or more new-lines may appear in a list instead of a semicolon, to delimit a command.

The first item of the first pipeline of a list that is a simple command not beginning with a redirection, and not occurring within a while, until, or if list, can be preceded by a semicolon. This semicolon is ignored unless the showme option is enabled as described with the set built-in below. (so it's decorative until it's not 🙈)

💖 the actual command forms

A command is either a simple-command or one of the following. Unless otherwise stated, the value returned by a command is that of the last simple-command executed in the command.

for vname [ in word ... ] ;do list ;done

Each time a for command is executed, vname is set to the next word taken from the in word list. If in word ... is omitted, then the for command executes the do list once for each positional parameter that is set, starting from 1 (see Parameter Expansion below). Execution ends when there are no more words in the list.

for (( [expr1] ; [expr2] ; [expr3] )) ;do list ;done

The arithmetic expression expr1 is evaluated first (see Arithmetic evaluation below). The arithmetic expression expr2 is repeatedly evaluated until it evaluates to zero, and when non-zero, list is executed and the arithmetic expression expr3 evaluated. If any expression is omitted, then it behaves as if it evaluated to 1. C-style for loop, we been knew 💫

select vname [ in word ... ] ;do list ;done

A select command prints on standard error (file descriptor 2) the set of words, each preceded by a number. If in word ... is omitted, then the positional parameters starting from 1 are used instead (see Parameter Expansion below). The PS3 prompt is printed and a line is read from the standard input.

If this line consists of the number of one of the listed words, then the value of the variable vname is set to the word corresponding to this number. If this line is empty, the selection list is printed again. Otherwise the value of the variable vname is set to null.

The contents of the line read from standard input is saved in the variable REPLY. The list is executed for each selection until a break or end-of-file is encountered. If the REPLY variable is set to null by the execution of list, then the selection list is printed before displaying the PS3 prompt for the next selection. it's a menu, it's interactive, it's iconic 🍓

case word in [ [(]pattern [ | pattern ] ... ) list ;; ] ... esac

A case command executes the list associated with the first pattern that matches word. The form of the patterns is the same as that used for file-name generation (see File Name Generation below). The ;; operator causes execution of case to terminate. If ;& is used in place of ;; the next subsequent list, if any, is executed. (fall-through! spooky! 💀)

if list ;then list [ ;elif list ;then list ] ... [ ;else list ] ;fi

The list following if is executed and, if it returns a zero exit status, the list following the first then is executed. Otherwise, the list following elif is executed and, if its value is zero, the list following the next then is executed. Failing each successive elif list, the else list is executed. If the if list has non-zero exit status and there is no else list, then the if command returns a zero exit status. (yes, that last bit is real, don't @ me)

while list ;do list ;done until list ;do list ;done

A while command repeatedly executes the while list and, if the exit status of the last command in the list is zero, executes the do list; otherwise the loop terminates. If no commands in the do list are executed, then the while command returns a zero exit status; until may be used in place of while to negate the loop termination test. 🔁

((expression))

The expression is evaluated using the rules for arithmetic evaluation described below. If the value of the arithmetic expression is non-zero, the exit status is 0, otherwise the exit status is 1.

(list)

Execute list in a separate environment. Note, that if two adjacent open parentheses are needed for nesting, a space must be inserted to avoid evaluation as an arithmetic command as described above. ⚠️ that's a real gotcha, bestie

{ list;}

list is simply executed. Note that unlike the metacharacters ( and ), { and } are reserved words and must occur at the beginning of a line or after a ; in order to be recognized. they're picky about their entrance 💅

[[ expression ]]

Evaluates expression and returns a zero exit status when expression is true. See Conditional Expressions below, for a description of expression.

function varname { list ;} varname () { list ;}

Define a function which is referenced by varname. A function whose varname contains a . is called a discipline function and the portion of the varname preceding the last . must refer to an existing variable. The body of the function is the list of commands between { and }. A function defined with the function varname syntax can also be used as an argument to the . special built-in command to get the equivalent behavior as if the varname() syntax were used to define it. (See Functions below.)

namespace identifier { list ;}

Defines or uses the name space identifier and runs the commands in list in this name space. (See Name Spaces below.)

& [ name [ arg... ] ]

Causes subsequent list commands terminated by & to be placed in the background job pool name. If name is omitted a default unnamed pool is used. Commands in a named background pool may be executed remotely. 👀 remote? we love reach

time [ pipeline ]

If pipeline is omitted the user and system time for the current shell and completed child processes is printed on standard error. Otherwise, pipeline is executed and the elapsed time as well as the user and system time are printed on standard error. The TIMEFORMAT variable may be set to a format string that specifies how the timing information should be displayed. See Shell Variables below for a description of the TIMEFORMAT variable. ⏱️✨

Okay so reserved words are only reserved when they’re the first word of a command and they’re not quoted — that’s the whole rule, bestie:

if then else elif fi case esac for while until do done { } function select time [[ ]] !

💖 Variable Assignments 💖

One or more variable assignments can start a simple command, or they can be arguments to the typeset, enum, export, or readonly special built-in commands — and also to other declaration commands created as types. ✨ The syntax is giving:

varname=word
varname[word]=word

No space is permitted between varname and the = or between = and word. No cap, zero spaces there.

varname=(assign_list)

No space is permitted between varname and the =. The variable varname is unset before the assignment. An assign_list can be one of these:

word ... — Indexed array assignment. 💅
[word]=word ... — Associative array assignment. If preceded by typeset -a this will create an indexed array instead.
assignment ... — Compound variable assignment. This creates a compound variable varname with sub-variables of the form varname.name, where name is the name portion of assignment. The value of varname will contain all the assignment elements. Additional assignments made to sub-variables of varname will also be displayed as part of the value of varname. If no assignments are specified, varname will be a compound variable allowing subsequence child elements to be defined.
typeset [options] assignment ... — Nested variable assignment. Multiple assignments can be specified by separating each of them with a ;. The previous value is unset before the assignment. Other declaration commands such as readonly, enum, and other declaration commands can be used in place of typeset.
. filename — Include the assignment commands contained in filename.

In addition, a += can be used in place of the = to signify adding to or appending to the previous value. When += is applied to an arithmetic type, word is evaluated as an arithmetic expression and added to the current value. When applied to a string variable, the value defined by word is appended to the value. For compound assignments, the previous value is not unset and the new values are appended to the current ones provided that the types are compatible. 🫶

The right hand side of a variable assignment undergoes all the expansion listed below except word splitting, brace expansion, and file name generation. When the left hand side of an assignment is a compound variable and the right hand is the name of a compound variable, the compound variable on the right will be copied or appended to the compound variable on the left. That’s the copy/paste energy but for shell variables.

💬 Comments 💬

A word beginning with # causes that word and all the following characters up to a new-line to be ignored. Basically the shell sees # and goes “not me reading the rest of this line 💀”.

🪄 Aliasing 🪄

The first word of each command is replaced by the text of an alias if an alias for this word has been defined. An alias name consists of any number of characters excluding metacharacters, quoting characters, file expansion characters, parameter expansion and command substitution characters, the characters / and =. The replacement string can contain any valid shell script including the metacharacters listed above. The first word of each command in the replaced text, other than any that are in the process of being replaced, will be tested for aliases. If the last character of the alias value is a blank then the word following the alias will also be checked for alias substitution. Aliases can be used to redefine built-in commands but cannot be used to redefine the reserved words listed above. Aliases can be created and listed with the alias command and can be removed with the unalias command.

Important plot twist: aliasing is performed when scripts are read, not while they are executed. Therefore, for an alias to take effect, the alias definition command has to be executed before the command which references the alias is read. Order matters, bestie — the alias has to be on the scene before the command shows up.

The following aliases are compiled into the shell but can be unset or redefined:

autoload=′typeset -fu′
command=′command  ′
compound=′typeset -C′
fc=hist
float=′typeset -lE′
functions=′typeset -f′
hash=′alias -t --′
history=′hist -l′
integer=′typeset -li′
nameref=′typeset -n′
nohup=′nohup  ′
r=′hist -s′
redirect=′command exec′
source=′command .′
stop=′kill -s STOP′
suspend=′kill -s STOP $$′
times=′{ { time;} 2>&1;}′
type=′whence -v′

🏠 Tilde Substitution 🏠

After alias substitution is performed, each word is checked to see if it begins with an unquoted ~. For tilde substitution, word also refers to the word portion of parameter expansion (see Parameter Expansion below). If it does, then the word up to a / is checked to see if it matches a user name in the password database (See getpwname(3).) If a match is found, the ~ and the matched login name are replaced by the login directory of the matched user. If no match is found, the original text is left unchanged. A ~ by itself, or in front of a /, is replaced by $HOME. A ~ followed by a + or - is replaced by the value of $PWD and $OLDPWD respectively. 🏡

In addition, when expanding a variable assignment, tilde substitution is attempted when the value of the assignment begins with a ~, and when a ~ appears after a :. The : also terminates a ~ login name. Colon said “that’s a wrap” on the login name.

📥 Command Substitution 📥

The standard output from a command list enclosed in parentheses preceded by a dollar sign ($(list)), or in a brace group preceded by a dollar sign (${ list;}), or in a pair of grave accents, may be used as part or all of a word; trailing new-lines are removed. In the second case, the { and } are treated as a reserved words so that { must be followed by a blank and } must appear at the beginning of the line or follow a ;. In the third (obsolete) form, the string between the quotes is processed for special quoting characters before the command is executed (see Quoting below). The command substitution $(cat file) can be replaced by the equivalent but faster $(<file). The command substitution $(n<#) will expand to the current byte offset for file descriptor n. Except for the second form, the command list is run in a subshell so that no side effects are possible. For the second form, the final } will be recognized as a reserved word after any token. ⭐

🧮 Arithmetic Substitution 🧮

An arithmetic expression enclosed in double parentheses preceded by a dollar sign ($(())) is replaced by the value of the arithmetic expression within the double parentheses. Math but make it shell, periodt.

🔀 Process Substitution 🔀

Each command argument of the form <(list) or >(list) will run process list asynchronously connected to some file in /dev/fd if this directory exists, or else a fifo in a temporary directory. The name of this file will become the argument to the command. If the form with > is selected then writing on this file will provide input for list. If < is used, then the file passed as an argument will contain the output of the list process. For example:

paste <(cut -f1 file1) <(cut -f3 file2) | tee >(process1) >(process2)

cuts fields 1 and 3 from the files file1 and file2 respectively, pastes the results together, and sends it to the processes process1 and process2, as well as putting it onto the standard output. Note that the file, which is passed as an argument to the command, is a UNIX pipe(2) so programs that expect to lseek(2) on the file will not work. ⚠️ If it needs to lseek(2), it’s gonna have a bad time.

Process substitution of the form <(list) can also be used with the < redirection operator which causes the output of list to be standard input or the input for whatever file descriptor is specified. Pipes, but make it fancy ✨

🧩 Parameter Expansion 🧩

A parameter is a variable, one or more digits, or any of the characters *, @, #, ?, -, $, and !. A variable is denoted by a vname. To create a variable whose vname contains a ., a variable whose vname consists of everything before the last . must already exist. A variable has a value and zero or more attributes. Variables can be assigned values and attributes by using the typeset special built-in command. The attributes supported by the shell are described later with the typeset special built-in command. Exported variables pass values and attributes to the environment. 💜

The shell supports both indexed and associative arrays. An element of an array variable is referenced by a subscript. A subscript for an indexed array is denoted by an arithmetic expression (see Arithmetic evaluation below) between a [ and a ]. To assign values to an indexed array, use vname=(value ...) or set -A vname value ... . The value of all non-negative subscripts must be in the range of 0 through 4,194,303. A negative subscript is treated as an offset from the maximum current index +1 so that -1 refers to the last element. Indexed arrays can be declared with the -a option to typeset. Indexed arrays need not be declared. Any reference to a variable with a valid subscript is legal and an array will be created if necessary. 🍓

An associative array is created with the -A option to typeset. A subscript for an associative array is denoted by a string enclosed between [ and ].

Referencing any array without a subscript is equivalent to referencing the array with subscript 0.

The value of a variable may be assigned by writing:

vname=value [ vname=value ] ...

or
       vname[subscript]=value [ vname[subscript]=value ] ...

okay so real talk: no space is allowed before or after the = 🫶 like, none. zero. not even one little space, bestie, the shell will simply not vibe with it.

Attributes you assign with the typeset special built-in command apply to all the elements of the array — the whole squad gets the same treatment, no cap. And an array element can be a simple variable, a compound variable, or an array variable. An element of an indexed array can be either an indexed array or an associative array. An element of an associative array can also be either. it's giving infinite nesting potential, honestly iconic 💅

To refer to an array element that is part of an array element, you just concatenate the subscript in brackets. For example, to refer to the foobar element of an associative array that is defined as the third element of the indexed array, use:

${vname[3][foobar]}

A nameref is a variable that is a reference to another variable ✨ It's created with the -n attribute of typeset. The value of the variable at the time of the typeset command becomes the variable that will be referenced whenever the nameref variable is used. The name of a nameref cannot contain a .. When a variable or function name contains a ., and the portion of the name up to the first . matches the name of a nameref, the variable referred to is obtained by replacing the nameref portion with the name of the variable referenced by the nameref. If a nameref is used as the index of a for loop, a name reference is established for each item in the list 🔁

A nameref provides a convenient way to refer to the variable inside a function whose name is passed as an argument to a function. For example, if the name of a variable is passed as the first argument to a function, the command

typeset -n var=$1

inside the function causes references and assignments to var to be references and assignments to the variable whose name has been passed to the function. chef's kiss, honestly 👑

If any of the floating point attributes, -E, -F, or -X, or the integer attribute, -i, is set for vname, then the value is subject to arithmetic evaluation as described below. math girl hours 🔥

Positional parameters, parameters denoted by a number, may be assigned values with the set special built-in command. Parameter $0 is set from argument zero when the shell is invoked.

The character $ is used to introduce substitutable parameters 💖

${parameter} — the shell reads all the characters from ${ to the matching } as part of the same word even if it contains braces or metacharacters. The value, if any, of the parameter is substituted. The braces are required when parameter is followed by a letter, digit, or underscore that is not to be interpreted as part of its name, when the variable name contains a .. The braces are also required when a variable is subscripted unless it is part of an Arithmetic Expression or a Conditional Expression. If parameter is one or more digits then it is a positional parameter. A positional parameter of more than one digit must be enclosed in braces. If parameter is ∗ or @, then all the positional parameters, starting with $1, are substituted (separated by a field separator character). If an array vname with last subscript ∗ @, or for index arrays of the form sub1 .. sub2. is used, then the value for each of the elements between sub1 and sub2 inclusive (or all elements for ∗ and @) is substituted, separated by the first character of the value of IFS.
${#parameter} — if parameter is ∗ or @, the number of positional parameters is substituted. Otherwise, the length of the value of the parameter is substituted. count 'em, bestie 🔢
${#vname[*]} ${#vname[@]} — the number of elements in the array vname is substituted. yes, both forms, they're the same vibe here 🎀
${@vname} — expands to the type name (See Type Variables below) or attributes of the variable referred to by vname.
${!vname} — expands to the name of the variable referred to by vname. This will be vname except when vname is a name reference. sneaky little indirection moment 😭
${!vname[subscript]} — expands to name of the subscript unless subscript is *, @. or of the form sub1 .. sub2. When subscript is *, the list of array subscripts for vname is generated. For a variable that is not an array, the value is 0 if the variable is set. Otherwise it is null. When subscript is @, same as above, except that when used in double quotes, each array subscript yields a separate argument. When subscript is of the form sub1 .. sub2 it expands to the list of subscripts between sub1 and sub2 inclusive using the same quoting rules as @.
${!prefix*} — expands to the names of the variables whose names begin with prefix. prefix girlies rise 🌸

okay now the good stuff, the conditional expansions 💜

${parameter:-word} — if parameter is set and is non-null then substitute its value; otherwise substitute word.
${parameter:=word} — if parameter is not set or is null then set it to word; the value of the parameter is then substituted. Positional parameters may not be assigned to in this way. like, hard no on that one 🙈
${parameter:?word} — if parameter is set and is non-null then substitute its value; otherwise, print word and exit from the shell (if not interactive). If word is omitted then a standard message is printed. dramatic exit, honestly 💀
${parameter:+word} — if parameter is set and is non-null then substitute word; otherwise substitute nothing.

In the above, word is not evaluated unless it is to be used as the substituted string, so that, in the following example, pwd is executed only if d is not set or is null:

print ${d:-$(pwd)}

If the colon (:) is omitted from the above expressions, then the shell only checks whether parameter is set or not. lowkey a big difference, don't sleep on it ⭐

${parameter:offset:length} ${parameter:offset} — expands to the portion of the value of parameter starting at the character (counting from 0) determined by expanding offset as an arithmetic expression and consisting of the number of characters determined by the arithmetic expression defined by length. In the second form, the remainder of the value is used. A negative offset counts backwards from the end of parameter. Note that one or more blanks is required in front of a minus sign to prevent the shell from interpreting the operator as :-. If parameter is ∗ or @, or is an array name indexed by ∗ or @, then offset and length refer to the array index and number of elements respectively. A negative offset is taken relative to one greater than the highest subscript for indexed arrays. The order for associate arrays is unspecified. unspecified, bestie, so don't come for me if it's weird 🦋
${parameter#pattern} ${parameter##pattern} — if the shell pattern matches the beginning of the value of parameter, then the value of this expansion is the value of the parameter with the matched portion deleted; otherwise the value of this parameter is substituted. In the first form the smallest matching pattern is deleted and in the second form the largest matching pattern is deleted. When parameter is @, *, or an array variable with subscript @ or *, the substring operation is applied to each element in turn. one # = smallest, two ## = biggest, write that down 📝
${parameter%pattern} ${parameter%%pattern} — if the shell pattern matches the end of the value of parameter, then the value of this expansion is the value of the parameter with the matched part deleted; otherwise substitute the value of parameter. In the first form the smallest matching pattern is deleted and in the second form the largest matching pattern is deleted. When parameter is @, *, or an array variable with subscript @ or *, the substring operation is applied to each element in turn. same energy, but from the back 🎀
${parameter/pattern/string} ${parameter//pattern/string} ${parameter/#pattern/string} ${parameter/%pattern/string} — expands parameter and replaces the longest match of pattern with the given string. Each occurrence of \n in string is replaced by the portion of parameter that matches the n-th sub-pattern. In the first form, only the first occurrence of pattern is replaced. In the second form, each match for pattern is replaced by the given string. The third form restricts the pattern match to the beginning of the string while the fourth form restricts the pattern match to the end of the string. When string is null, the pattern will be deleted and the / in front of string may be omitted. When parameter is @, *, or an array variable with subscript @ or *, the substitution operation is applied to each element in turn. In this case, the string portion of word will be re-evaluated for each element. four forms, all baddies, all valid 💅✨

The following parameters are literally just handed to you by the shell — you don't set them, they set themselves, and honestly? iconic behavior:

# — the number of positional parameters, in decimal. ✨
- — the options you handed the shell when you invoked it, or the ones you set later with the set command.
? — the decimal value that the last executed command returned. your fave little "did it work tho" number 💅
$ — the process number of this shell. that's your shell's ID, bestie.
_ — okay this one is doing the absolute most, buckle up 🎀:
- At first, the value of _ is an absolute pathname of the shell or script being executed, as passed in through the environment.
- After that, it gets assigned the last argument of the previous command.
- It is not set for commands that are asynchronous.
- It's also the parameter that holds the name of the matching MAIL file when checking for mail.
- While you're defining a compound variable or a type, _ is initialized as a reference to the compound variable or type.
- When a discipline function is invoked, _ is initialized as a reference to the variable associated with the call to that function.
- And finally, when _ is used as the name of the first variable of a type definition, the new type is derived from the type of that first variable (see Type Variables below).
! — the process id, or the pool name and job number, of the last background command you invoked, or the most recent job you shoved into the background with the bg built-in command. Background jobs started in a named pool come out looking like pool.number, where pool is the pool name and number is the job number within that pool. no cap.
.sh.command — when processing a DEBUG trap, this variable holds the current command line that's about to run.
.sh.edchar — holds the value of the keyboard character (or sequence of characters, if the first character is an ESC, ascii 033) that's been entered while processing a KEYBD trap (see Key Bindings below). If you change the value as part of the trap action, then the new value replaces the key (or key sequence) that caused the trap. swapping the vibes fr fr.
.sh.edcol — the character position of the cursor at the time of the most recent KEYBD trap.
.sh.edmode — the value is set to ESC when processing a KEYBD trap while in vi insert mode. (See Vi Editing Mode below.) Otherwise, .sh.edmode is null when processing a KEYBD trap.
.sh.edtext — the characters sitting in the input buffer at the time of the most recent KEYBD trap. The value is null when you're not processing a KEYBD trap.
.sh.file — the pathname of the file that contains the current command.
.sh.fun — the name of the current function that's being executed.
.sh.level — set to the current function depth. You can change it inside a DEBUG trap, and it'll set the context to the level you specified. yes bestie you can just do that.
.sh.lineno — set during a DEBUG trap to the line number for the caller of each function.
.sh.match — an indexed array that stores the most recent match and sub-pattern matches, after conditional pattern matches that match and after variable expansions using the operators #, %, or /. The 0-th element stores the complete match, and the i-th element stores the i-th submatch. The .sh.match variable becomes unset when the variable that has expanded is assigned a new value.
.sh.math — used for defining arithmetic functions (see Arithmetic evaluation below), and it stores the list of user defined arithmetic functions.
.sh.name — set to the name of the variable at the time that a discipline function is invoked.
.sh.subscript — set to the name subscript of the variable at the time that a discipline function is invoked.
.sh.subshell — the current depth for subshells and command substitution.
.sh.value — set to the value of the variable at the time that the set or append discipline function is invoked. When a user defined arithmetic function is invoked, the value of .sh.value is saved and .sh.value is set to long double precision floating point. .sh.value is restored when the function returns. 💖
.sh.version — set to a value that identifies the version of this shell.
KSH_VERSION — a name reference to .sh.version.
LINENO — the current line number within the script or function being executed.
OLDPWD — the previous working directory, set by the cd command.
OPTARG — the value of the last option argument processed by the getopts built-in command.
OPTIND — the index of the last option argument processed by the getopts built-in command.
PPID — the process number of the parent of the shell. hi mom 🫶
PWD — the present working directory, set by the cd command.
RANDOM — every single time this variable is referenced, a random integer that's uniformly distributed between 0 and 32767 gets generated. You can initialize the sequence of random numbers by assigning a numeric value to RANDOM. slay, controlled chaos. 🔥
REPLY — this variable is set by the select statement and by the read built-in command when no arguments are supplied.
SECONDS — each time this variable is referenced, the number of seconds since shell invocation is returned. If you assign a value to this variable, then the value returned upon reference will be the value you assigned plus the number of seconds since the assignment. math girlie behavior tbh.
SHLVL — an integer variable that is incremented each time the shell is invoked, and it's exported. If SHLVL isn't in the environment when the shell is invoked, it's set to 1.

Okay so, continuing the variable tour: the shell uses these, and every single one matters. No cap. 🫶

CDPATH — the search path for the cd command. Your “where can I go” list, basically.
COLUMNS — if this is set, its value defines the width of the edit window for the shell edit modes and for printing select lists. Very demure, very formatting-aware. ✨
EDITOR — if VISUAL is not set, the shell checks this value against the patterns described with VISUAL below, and turns on the corresponding editing option (see Special Command set below). So yes, it’s doing real work.
ENV — if this is set, then parameter expansion, command substitution, and arithmetic substitution are performed on the value to generate the pathname of the script that will be executed when the shell is invoked interactively (see Invocation below). This file is typically used for alias and function definitions. The default value is $HOME/.kshrc. On systems that support a system wide /etc/ksh.kshrc initialization file, if the filename generated by the expansion of ENV begins with /./ or ./. the system wide initialization file will not be executed. Messy? A little. Important? Extremely. 💅
FCEDIT — obsolete name for the default editor name for the hist command. FCEDIT is not used when HISTEDIT is set. It’s giving legacy icon behavior.
FIGNORE — a pattern that defines the set of filenames that will be ignored when performing filename matching. Bye, irrelevant files.
FPATH — the search path for function definitions. The directories in this path are searched for a file with the same name as the function or command when a function with the -u attribute is referenced and when a command is not found. If an executable file with the name of that command is found, then it is read and executed in the current environment. Unlike PATH, the current directory must be represented explicitly by . rather than by adjacent : characters or a beginning or ending :. Ma’am is strict about this one.
HISTCMD — number of the current command in the history file. Your little timestamp in the group chat, but for commands.
HISTEDIT — name for the default editor name for the hist command.
HISTFILE — if this variable is set when the shell is invoked, then the value is the pathname of the file that will be used to store the command history (see Command Re-entry below). Your receipts, saved.
HISTSIZE — if this variable is set when the shell is invoked, then the number of previously entered commands that are accessible by this shell will be greater than or equal to this number. The default is 512. So many little memories.
HOME — the default argument (home directory) for the cd command. The place you always end up back at, bestie.
IFS — internal field separators, normally space, tab, and new-line that are used to separate the results of command substitution or parameter expansion and to separate fields with the built-in command read. The first character of the IFS variable is used to separate arguments for the "$∗" substitution (see Quoting below). Each single occurrence of an IFS character in the string to be split, that is not in the isspace character class, and any adjacent characters in IFS that are in the isspace character class, delimit a field. One or more characters in IFS that belong to the isspace character class, delimit a field. In addition, if the same isspace character appears consecutively inside IFS, this character is treated as if it were not in the isspace class, so that if IFS consists of two tab characters, then two adjacent tab characters delimit a null field. This is the moment where shell girlies start speaking in whisper tones. 😭
JOBMAX — this variable defines the maximum number running background jobs that can run at a time. When this limit is reached, the shell will wait for a job to complete before starting a new job. Queue behavior, but make it background jobs.
LANG — this variable determines the locale category for any category not specifically selected with a variable starting with LC_ or LANG.
LC_ALL — this variable overrides the value of the LANG variable and any other LC_ variable. The final boss of locale settings.
LC_COLLATE — this variable determines the locale category for character collation information. Sorting vibes only. 🌸
LC_CTYPE — this variable determines the locale category for character handling functions. It determines the character classes for pattern matching (see File Name Generation below).
LC_NUMERIC — this variable determines the locale category for the decimal point character. Let the decimal point be it.
LINES — if this variable is set, the value is used to determine the column length for printing select lists. Select lists will print vertically until about two-thirds of LINES lines are filled. Cute and space-conscious.
MAIL — if this variable is set to the name of a mail file and the MAILPATH variable is not set, then the shell informs the user of arrival of mail in the specified file. Old-school notifs, but make it mail.
MAILCHECK — this variable specifies how often (in seconds) the shell will check for changes in the modification time of any of the files specified by the MAILPATH or MAIL variables. The default value is 600 seconds. When the time has elapsed the shell will check before issuing the next prompt. Slow and steady, but it does check.
MAILPATH — a colon (:) separated list of file names. If this variable is set, then the shell informs the user of any modifications to the specified files that have occurred within the last MAILCHECK seconds. Each file name can be followed by a ? and a message that will be printed. The message will undergo parameter expansion, command substitution, and arithmetic substitution with the variable $_ defined as the name of the file that has changed. The default message is you have mail in $_. She’s dramatic, but she’s correct.
PATH — the search path for commands (see Execution below). The user may not change PATH if executing under rksh (except in .profile). Restricted shell says no, thank you. 🙅
PS1 — the value of this variable is expanded for parameter expansion, command substitution, and arithmetic substitution to define the primary prompt string which by default is $. The character ! in the primary prompt string is replaced by the command number (see Command Re-entry below). Two successive occurrences of ! will produce a single ! when the prompt string is printed. Prompt gets a little lore.
PS2 — secondary prompt string, by default > . Continuation line, but make it serve.
PS3 — selection prompt string used within a select loop, by default #? . The choose-your-own-adventure prompt.
PS4 — the value of this variable is expanded for parameter evaluation, command substitution, and arithmetic substitution and precedes each line of an execution trace. By default, PS4 is + . In addition when PS4 is unset, the execution trace prompt is also + . The debugging bestie. 🔥
SHELL — the pathname of the shell is kept in the environment. At invocation, if the basename of this variable is rsh, rksh, or krsh, then the shell becomes restricted. If it is pfsh or pfksh, then the shell becomes a profile shell (see pfexec(1)). Shell identity crisis, but make it intentional.
TIMEFORMAT — the value of this parameter is used as a format string specifying how the timing information for pipelines prefixed with the time reserved word should be displayed. The % character introduces a format sequence that is expanded to a time value or other information. The format sequences and their meanings are as follows.
- %% — a literal %.
- %[p][l]R — the elapsed time in seconds.
- %[p][l]U — the number of CPU seconds spent in user mode.
- %[p][l]S — the number of CPU seconds spent in system mode.
- %P — the CPU percentage, computed as (U + S) / R.

The brackets denote optional portions. The optional p is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output. At most three places after the decimal point can be displayed; values of p greater than 3 are treated as 3. If p is not specified, the value 3 is used.

The optional l specifies a longer format, including hours if greater than zero, minutes, and seconds of the form HHhMMmSS.FFs. The value of p determines whether or not the fraction is included.

All other characters are output without change and a trailing newline is added. If unset, the default value, $'\nreal\t%2lR\nuser\t%2lU\nsys%2lS', is used. If the value is null, no timing information is displayed. Timing info said “I’m the main character.” ⏱️

TMOUT — if set to a value greater than zero, TMOUT will be the default timeout value for the read built-in command. The select compound command terminates after TMOUT seconds when input is from a terminal. Otherwise, the shell will terminate if a line is not entered within the prescribed number of seconds while reading from a terminal.

heads up, bestie: the shell can be compiled with a maximum bound for this value which cannot be exceeded. So no, you cannot just set it to a billion and call it a day. 💀

VISUAL — if the value of this variable matches the pattern *[Vv][Ii]*, then the vi option (see Special Command set below) is turned on. If the value matches the pattern *gmacs*, the gmacs option is turned on. If the value matches the pattern *macs*, then the emacs option will be turned on. The value of VISUAL overrides the value of EDITOR. Editor war, but the shell already picked a side. 👑

The shell hands out default values to PATH, PS1, PS2, PS3, PS4, MAILCHECK, FCEDIT, TMOUT and IFS, while HOME, SHELL, ENV, and MAIL are not set at all by the shell (although HOME is set by login(1)). On some systems MAIL and SHELL are also set by login(1).

🌸 Field Splitting 🌸

After parameter expansion and command substitution, the results of substitutions are scanned for the field separator characters (those found in IFS) and split into distinct fields where such characters are found. Explicit null fields ("" or ′′) are retained. Implicit null fields (those resulting from parameters that have no values or command substitutions with no output) are removed.

If the braceexpand (-B) option is set then each of the fields resulting from IFS are checked to see if they contain one or more of the brace patterns {*,*}, {l1..l2}, {n1..n2}, {n1..n2% fmt}, {n1..n2 ..n3}, or {n1..n2 ..n3%fmt}, where * represents any character, l1,l2 are letters and n1,n2,n3 are signed numbers and fmt is a format specified as used by printf. In each case, fields are created by prepending the characters before the { and appending the characters after the } to each of the strings generated by the characters between the { and }. The resulting fields are checked to see if they have any brace patterns.

In the first form, a field is created for each string between { and ,, between , and ,, and between , and }. The string represented by * can contain embedded matching { and } without quoting. Otherwise, each { and } with * must be quoted.

In the “seconds” form, l1 and l2 must both be either upper case or both be lower case characters in the C locale. In this case a field is created for each character from l1 thru l2.

In the remaining forms, a field is created for each number starting at n1 and continuing until it reaches n2 incrementing n1 by n3. When n3 is not specified, it behaves as if n3 were 1 if n1<=n2 and -1 otherwise. If a form specifies %fmt, any format flags, widths and precisions can be specified and fmt can end in any of the specifiers cdiouxX. For example, {a,z}{1..5..3%02d}{b..c}x expands to the 8 fields, a01bx, a01cx, a04bx, a04cx, z01bx, z01cx, z04bx and z4cx.

🦋 File Name Generation 🦋

Following splitting, each field is scanned for the characters ∗, ?, (, and [ unless the -f option has been set. If one of these characters appears, then the word is regarded as a pattern. Each file name component that contains any pattern character is replaced with a lexicographically sorted set of names that matches the pattern from that directory. If no file name is found that matches the pattern, then that component of the filename is left unchanged unless the pattern is prefixed with ∼(N) in which case it is removed as described below. If FIGNORE is set, then each file name component that matches the pattern defined by the value of FIGNORE is ignored when generating the matching filenames. The names . and .. are also ignored. If FIGNORE is not set, the character . at the start of each file name component will be ignored unless the first character of the pattern corresponding to this component is the character . itself. Note, that for other uses of pattern matching the / and . are not treated specially.

∗ — Matches any string, including the null string. When used for filename expansion, if the globstar option is on, two adjacent ∗'s by itself will match all files and zero or more directories and subdirectories. If followed by a / then only directories and subdirectories will match.
? — Matches any single character.
[...] — Matches any one of the enclosed characters. A pair of characters separated by - matches any character lexically between the pair, inclusive. If the first character following the opening [ is a ! or ^ then any character not enclosed is matched. A - can be included in the character set by putting it as the first or last character. Within [ and ], character classes can be specified with the syntax [:class:] where class is one of the following classes defined in the ANSI-C standard: (Note that word is equivalent to alnum plus the character _.)

alnum alpha blank cntrl digit graph lower print punct
space upper word xdigit

Within [ and ], an equivalence class can be specified with the syntax [=c=] which matches all characters with the same primary collation weight (as defined by the current locale) as the character c. Within [ and ], [.symbol.] matches the collating symbol symbol.

A pattern-list is a list of one or more patterns separated from each other with a & or ⎪. A & signifies that all patterns must be matched whereas ⎪ requires that only one pattern be matched. Composite patterns can be formed with one or more of the following sub-patterns:

?(pattern-list) — Optionally matches any one of the given patterns.
*(pattern-list) — Matches zero or more occurrences of the given patterns.
+(pattern-list) — Matches one or more occurrences of the given patterns.
{n}(pattern-list) — Matches n occurrences of the given patterns.
{m,n}(pattern-list) — Matches from m to n occurrences of the given patterns. If m is omitted, 0 will be used. If n is omitted at least m occurrences will be matched.
@(pattern-list) — Matches exactly one of the given patterns.
!(pattern-list) — Matches anything except one of the given patterns.

By default, each pattern, or sub-pattern will match the longest string possible consistent with generating the longest overall match. If more than one match is possible, the one starting closest to the beginning of the string will be chosen. However, for each of the above compound patterns a - can be inserted in front of the ( to cause the shortest match to the specified pattern-list to be used.

When pattern-list is contained within parentheses, the backslash character \ is treated specially even when inside a character class. All ANSI-C character escapes are recognized and match the specified character. In addition the following escape sequences are recognized:

\d — Matches any character in the digit class.
\D — Matches any character not in the digit class.
\s — Matches any character in the space class.
\S — Matches any character not in the space class.
\w — Matches any character in the word class.
\W — Matches any character not in the word class.

A pattern of the form %(pattern-pair(s)) is a sub-pattern that can be used to match nested character expressions. Each pattern-pair is a two character sequence which cannot contain & or ⎪. The first pattern-pair specifies the starting and ending characters for the match. Each subsequent pattern-pair represents the beginning and ending characters of a nested group that will be skipped over when counting starting and ending character matches. The behavior is unspecified when the first character of a pattern-pair is alpha-numeric except for the following:

D — Causes the ending character to terminate the search for this pattern without finding a match.
E — Causes the ending character to be interpreted as an escape character.
L — Causes the ending character to be interpreted as a quote character causing all characters to be ignored when looking for a match.
Q — Causes the ending character to be interpreted as a quote character causing all characters other than any escape character to be ignored when looking for a match.

Thus, %({}Q"E\), matches characters starting at { until the matching } is found not counting any { or } that is inside a double quoted string or preceded by the escape character \. Without the {} this pattern matches any C language string.

Each sub-pattern in a composite pattern is numbered, starting at 1, by the location of the ( within the pattern. The sequence \n, where n is a single digit and \n comes after the n-th sub-pattern, matches the same string as the sub-pattern itself.

Finally a pattern can contain sub-patterns of the form ∼(options:pattern-list), where either options or :pattern-list can be omitted. Unlike the other compound patterns, these sub-patterns are not counted in the numbered sub-patterns. :pattern-list must be omitted for options F, G, N, and V below. If options is present, it can consist of one or more of the following:

+ — Enable the following options. This is the default.
- — Disable the following options.
E — The remainder of the pattern uses extended regular expression syntax like the egrep(1) command.
F — The remainder of the pattern uses fgrep(1) expression syntax.
G — The remainder of the pattern uses basic regular expression syntax like the grep(1) command.
K — The remainder of the pattern uses shell pattern syntax. This is the default.
N — This is ignored. However, when it is the first letter and is used with file name generation, and no matches occur, the file pattern expands to the empty string.
X — The remainder of the pattern uses augmented regular expression syntax like the xgrep(1) command.
P — The remainder of the pattern uses perl(1) regular expression syntax. Not all perl regular expression syntax is currently implemented.
V — The remainder of the pattern uses System V regular expression syntax.
i — Treat the match as case insensitive.
g — File the longest match (greedy). This is the default.
l — Left anchor the pattern. This is the default for K style patterns.
r — Right anchor the pattern. This is the default for K style patterns.

If both options and :pattern-list are specified, then the options apply only to pattern-list. Otherwise, these options remain in effect until they are disabled by a subsequent ∼(...) or at the end of the sub-pattern containing ∼(...).

Quoting 💬✨

okay so, quoting time, bestie. Each of the metacharacters listed earlier (see Definitions above) has a special meaning to the shell and causes termination of a word unless quoted. A character may be quoted (i.e., made to stand for itself) by preceding it with a \. The pair \new-line is removed. All characters enclosed between a pair of single quote marks ('') that is not preceded by a $ are quoted. A single quote cannot appear within the single quotes. A single quoted string preceded by an unquoted $ is processed as an ANSI-C string except for the following:

\0 — causes the remainder of the string to be ignored.
\E — equivalent to the escape character (ascii 033).
\e — equivalent to the escape character (ascii 033).
\cx — expands to the character control-x.
\C[.name.] — expands to the collating element name.

Inside double quote marks (""), parameter and command substitution occur and \ quotes the characters \, the backtick character, ", and $. A $ in front of a double quoted string will be ignored in the "C" or "POSIX" locale, and may cause the string to be replaced by a locale specific string otherwise. The meaning of $∗ and $@ is identical when not quoted or when used as a variable assignment value or as a file name. However, when used as a command argument, "$∗" is equivalent to "$1d$2d...", where d is the first character of the IFS variable, whereas "$@" is equivalent to "$1" "$2" .... Inside grave quote marks (backticks), \ quotes \, a backtick, and $. If the grave quotes occur within double quotes, then \ also quotes the character ".

The special meaning of reserved words or aliases can be removed by quoting any character of the reserved word. The recognition of function names or built-in command names listed below cannot be altered by quoting them.

Arithmetic Evaluation 🧮💖

The shell performs arithmetic evaluation for arithmetic substitution, to evaluate an arithmetic command, to evaluate an indexed array subscript, and to evaluate arguments to the built-in commands shift and let. Evaluations are performed using double precision floating point arithmetic or long double precision floating point for systems that provide this data type. Floating point constants follow the ANSI-C programming language floating point conventions. The floating point constants Nan and Inf can be used to represent "not a number" and infinity respectively. Integer constants follow the ANSI-C programming language integer constant conventions although only single byte character constants are recognized and character casts are not recognized. In addition constants can be of the form [base#]n where base is a decimal number between two and sixty-four representing the arithmetic base and n is a number in that base. The digits above 9 are represented by the lower case letters, the upper case letters, @, and _ respectively. For bases less than or equal to 36, upper and lower case characters can be used interchangeably.

An arithmetic expression uses the same syntax, precedence, and associativity of expression as the C language. All the C language operators that apply to floating point quantities can be used. In addition, the operator ** can be used for exponentiation. It has higher precedence than multiplication and is left associative. In addition, when the value of an arithmetic variable or sub-expression can be represented as a long integer, all C language integer arithmetic operations can be performed. Variables can be referenced by name within an arithmetic expression without using the parameter expansion syntax. When a variable is referenced, its value is evaluated as an arithmetic expression.

Any of the following math library functions that are in the C math library can be used within an arithmetic expression:

abs acos acosh asin asinh atan atan2 atanh cbrt ceil copysign cos cosh
erf erfc exp exp2 expm1 fabs fpclassify fdim finite floor fma fmax fmin
fmod hypot ilogb int isfinite sinf isnan isnormal issubnormal
issubordered iszero j0 j1 jn lgamma log log10 log2 logb nearbyint
nextafter nexttoward pow remainder rint round scanb signbit sin sinh
sqrt tan tanh tgamma trunc y0 y1 yn

In addition, arithmetic functions can be defined as shell functions with a variant of the function name syntax,

function .sh.math.name ident ... { list ;}

where name is the function name used in the arithmetic expression and each identifier, ident is a name reference to the long double precision floating point argument. The value of .sh.value when the function returns is the value of this function. User defined functions can take up to 3 arguments and override C math library functions.

An internal representation of a variable as a double precision floating point can be specified with the -E [n], -F [n], or -X [n] option of the typeset special built-in command. The -E option causes the expansion of the value to be represented using scientific notation when it is expanded. The optional option argument n defines the number of significant figures. The -F option causes the expansion to be represented as a floating decimal number when it is expanded. The -X option causes the expansion to be represented using the %a format defined by ISO C-99. The optional option argument n defines the number of places after the decimal (or radix) point in this case.

An internal integer representation of a variable can be specified with the -i [n] option of the typeset special built-in command. The optional option argument n specifies an arithmetic base to be used when expanding the variable. If you do not specify an arithmetic base, base 10 will be used.

Arithmetic evaluation is performed on the value of each assignment to a variable with the -E, -F, -X, or -i attribute. Assigning a floating point number to a variable whose type is an integer causes the fractional part to be truncated.

Prompting 🎀🫶

When used interactively, the shell prompts with the value of PS1 after expanding it for parameter expansion, command substitution, and arithmetic substitution, before reading a command. In addition, each single ! in the prompt is replaced by the command number. A !! is required to place ! in the prompt. If at any time a new-line is typed and further input is needed to complete a command, then the secondary prompt (i.e., the value of PS2) is issued.

Conditional Expressions 🦋✨

A conditional expression is used with the [[ compound command to test attributes of files and to compare strings. Field splitting and file name generation are not performed on the words between [[ and ]]. Each expression can be constructed from one or more of the following unary or binary expressions:

string — true if string is not null.
-a file — same as -e below. This is obsolete.
-b file — true if file exists and is a block special file.
-c file — true if file exists and is a character special file.
-d file — true if file exists and is a directory.
-e file — true if file exists.
-f file — true if file exists and is an ordinary file.
-g file — true if file exists and it has its setgid bit set.
-k file — true if file exists and it has its sticky bit set.
-n string — true if length of string is non-zero.
-o ?option — true if option named option is a valid option name.
-o option — true if option named option is on.
-p file — true if file exists and is a fifo special file or a pipe.
-r file — true if file exists and is readable by current process.
-s file — true if file exists and has size greater than zero.
-t fildes — true if file descriptor number fildes is open and associated with a terminal device.
-u file — true if file exists and it has its setuid bit set.
-v name — true if variable name is a valid variable name and is set.
-w file — true if file exists and is writable by current process.
-x file — true if file exists and is executable by current process. If file exists and is a directory, then true if the current process has permission to search in the directory.
-z string — true if length of string is zero.
-L file — true if file exists and is a symbolic link.
-h file — true if file exists and is a symbolic link.
-N file — true if file exists and the modification time is greater than the last access time.
-O file — true if file exists and is owned by the effective user id of this process.
-G file — true if file exists and its group matches the effective group id of this process.
-R name — true if variable name is a name reference.
-S file — true if file exists and is a socket.
file1 -nt file2 — true if file1 exists and file2 does not, or file1 is newer than file2.
file1 -ot file2 — true if file2 exists and file1 does not, or file1 is older than file2.
file1 -ef file2 — true if file1 and file2 exist and refer to the same file.
string == pattern — true if string matches pattern. Any part of pattern can be quoted to cause it to be matched as a string. With a successful match to a pattern, the .sh.match array variable will contain the match and sub-pattern matches.
string = pattern — same as == above, but is obsolete.
string != pattern — true if string does not match pattern. When the string matches the pattern the .sh.match array variable will contain the match and sub-pattern matches.
string =∼ ere — true if string matches the pattern ∼(E)ere where ere is an extended regular expression.
string1 < string2 — true if string1 comes before string2 based on ASCII value of their characters.
string1 > string2 — true if string1 comes after string2 based on ASCII value of their characters.

The following obsolete arithmetic comparisons are also permitted:

exp1 -eq exp2 — true if exp1 is equal to exp2.
exp1 -ne exp2 — true if exp1 is not equal to exp2.
exp1 -lt exp2 — true if exp1 is less than exp2.
exp1 -gt exp2 — true if exp1 is greater than exp2.
exp1 -le exp2 — true if exp1 is less than or equal to exp2.
exp1 -ge exp2 — true if exp1 is greater than or equal to exp2.

In each of the above expressions, if file is of the form /dev/fd/n, where n is an integer, then the test is applied to the open file whose descriptor number is n. 💅

A compound expression can be built out of those primitives using any of the following — and yes, they're listed in decreasing order of precedence, so read top to bottom and respect the hierarchy 💅

(expression) — true if expression is true. It's the grouping move, aka the parentheses that keep your logic from falling apart ✨
! expression — true if expression is false. The little hater operator, we love her 💀
expression1 && expression2 — true only if expression1 and expression2 are both true. Both. No halfsies 🫶
expression1 || expression2 — true if either one of them is true. Lowkey the most forgiving one here 🌈

🎀 Input/Output 🎀

okay so before a command even runs, its input and output can get redirected using a special notation that the shell itself interprets. The following can show up anywhere in a simple-command, or before or after a command — and none of it gets passed on to the command you're invoking. Command substitution, parameter expansion, and arithmetic substitution all happen before word or digit is used, except where noted below. File name generation only kicks in if the shell is interactive and the pattern matches exactly one file. Field splitting? Not performed. Periodt.

In each of the redirections below, if file looks like /dev/sctp/host/port, /dev/tcp/host/port, or /dev/udp/host/port — where host is a hostname or host address and port is a service name or an integer port number — then the redirection tries to make a tcp, sctp, or udp connection to that socket. Iconic networking behavior ngl 🔥

⚠️ No intervening space is allowed between the characters of redirection operators. Like, zero. Not even one. Don't test her.

<word — use file word as standard input (file descriptor 0).
>word — use file word as standard output (file descriptor 1). If the file doesn't exist, it gets created. If the file does exist and the noclobber option is on, this throws an error; otherwise the file gets truncated to zero length 💀
>|word — same as >, except it overrides the noclobber option. She does not care about your rules 💅
>;word — write output to a temporary file. If the command completes successfully, rename it to word; otherwise, delete the temporary file. Note: >;word cannot be used with the exec(2) built-in.
>>word — use file word as standard output. If the file exists, output is appended to it (by first seeking to the end-of-file); otherwise the file is created. The "no thoughts just append" of redirection 🫶
<>word — open file word for reading and writing as standard output. Versatile queen.
<>;word — same as <>word except that if the command completes successfully, word is truncated to the offset at command completion. Also cannot be used with the exec(2) built-in.
<<[-]word — the shell input is read up to a line that's the same as word after any quoting is removed, or up to an end-of-file. No parameter substitution, command substitution, arithmetic substitution, or file name generation is performed on word. The resulting document — called a here-document — becomes standard input. If any character of word is quoted, then no interpretation is placed on the document's characters; otherwise, parameter expansion, command substitution, and arithmetic substitution occur, \new-line is ignored, and \ must be used to quote the characters \, $, and `. If - is appended to <<, then all leading tabs are stripped from word and from the document. If # is appended to <<, then leading spaces and tabs get stripped off the first line of the document, and up to an equivalent indentation gets stripped from the remaining lines and from word. A tab stop is assumed at every 8 columns when determining the indentation ✨
<<<word — a short form of here-document where word becomes the contents of the here-document after any parameter expansion, command substitution, and arithmetic substitution occur. The lil shortcut bestie 🎀
<&digit — standard input is duplicated from file descriptor digit (see dup(2)). Same energy for standard output using >&digit.
<&digit- — the file descriptor given by digit is moved to standard input. Similarly for standard output using >&digit-.
<&- — standard input is closed. Similarly for standard output using >&-.
<&p — the input from the co-process is moved to standard input.
>&p — the output to the co-process is moved to standard output.
<#((expr)) — evaluate the arithmetic expression expr and position file descriptor 0 to the resulting value in bytes from the start of the file. While evaluating expr, the variables CUR and EOF evaluate to the current offset and the end-of-file offset respectively 🔥
>#((offset)) — same as <# except it applies to file descriptor 1.
<#pattern — seeks forward to the beginning of the next line containing pattern.
<##pattern — same as <# except the portion of the file that gets skipped is copied to standard output. Not her being generous 😭

If one of the above is preceded by a digit, with no intervening space, then the file descriptor number referred to is the one that digit specifies (instead of the default 0 or 1). If one of the above — other than >&- and the ># and <# forms — is preceded by {varname} with no intervening space, then a file descriptor number > 10 will be selected by the shell and stored in the variable varname. And if >&- or any of the ># and <# forms is preceded by {varname}, then the value of varname defines the file descriptor to close or position 👑

For example:

... 2>&1

means file descriptor 2 is to be opened for writing as a duplicate of file descriptor 1, and

exec {n}<file

means open the file named file for reading and store the file descriptor number in the variable n ✨

The order in which redirections are specified is significant. The shell evaluates each redirection in terms of the (file descriptor, file) association at the time of evaluation. For example:

... 1>fname 2>&1

first associates file descriptor 1 with the file fname. It then associates file descriptor 2 with the file associated with file descriptor 1 (i.e. fname). If the order of redirections were reversed, file descriptor 2 would be associated with the terminal (assuming file descriptor 1 had been) and then file descriptor 1 would be associated with the file fname. Order matters, bestie. It's giving choreography 💅

If a command is followed by & and job control is not active, then the default standard input for the command is the empty file /dev/null. Otherwise, the environment for the execution of a command contains the file descriptors of the invoking shell as modified by the input/output specifications.

🌸 Environment 🌸

The environment (see environ(7)) is a list of name-value pairs that gets passed to an executed program the same way as a normal argument list. The names must be identifiers and the values are character strings. The shell interacts with the environment in several ways:

On invocation, the shell scans the environment and creates a variable for each name it finds, giving it the corresponding value and attributes and marking it export 🫶
Executed commands inherit the environment.
If the user modifies the values of these variables or creates new ones using the export or typeset -x commands, they become part of the environment.

So the environment any executed command sees is composed of any name-value pairs originally inherited by the shell (values possibly modified by the current shell) plus any additions noted in export or typeset -x commands.

The environment for any simple-command or function can be augmented by prefixing it with one or more variable assignments. A variable assignment argument is a word of the form identifier=value. So:

TERM=450 cmd args                  and
(export TERM; TERM=450; cmd args)

are equivalent — as far as the execution of cmd above is concerned — except for the special built-in commands listed below, those ones preceded with a dagger 😌

If the obsolete -k option is set, all variable assignment arguments are placed in the environment, even if they occur after the command name. The following first prints a=b c and then c:

echo a=b c
set -k
echo a=b c

🚨 This feature is intended for use with scripts written for early versions of the shell, and its use in new scripts is strongly discouraged. It is likely to disappear someday. Like, do not build anything on this. Fr fr.

🦋 Functions 🦋

For historical reasons there are two ways to define functions: the name() syntax and the function name syntax, both described in the Commands section above. Shell functions are read in and stored internally. Alias names are resolved when the function is read. Functions are executed like commands, with the arguments passed as positional parameters. (See Execution below.)

Functions defined with the function name syntax and called by name execute in the same process as the caller, and share all files and the present working directory with the caller. Traps caught by the caller are reset to their default action inside the function. A trap condition that is not caught or ignored by the function causes the function to terminate, and the condition gets passed on to the caller. A trap on EXIT set inside a function is executed in the environment of the caller after the function completes. Ordinarily, variables are shared between the calling program and the function — however, the typeset special built-in command used within a function defines local variables whose scope includes the current function. They can be passed to functions that they call in the variable assignment list that precedes the call, or as arguments passed as name references. Errors within functions return control to the caller 💜

Functions defined with the name() syntax, and functions defined with the function name syntax that are invoked with the . special built-in, are executed in the caller's environment and share all variables and traps with the caller. Errors within these function executions cause the script that contains them to abort 😭

The special built-in command return is used to return from function calls.

Function names can be listed with the -f or +f option of the typeset special built-in command. The text of functions, when available, will also be listed with -f. Functions can be undefined with the -f option of the unset special built-in command. Clean up after yourself, queen 👑

Okay so real talk: functions ghost you when the shell executes a shell script — that's just the default behaviour, no cap. Functions that need to be defined across separate invocations of the shell should live in a directory, and the FPATH variable should contain the name of that directory 💖. They may also be specified in the ENV file. Easy.

🎀 Discipline Functions 🎀

Every variable can have zero or more discipline functions attached to it — think of them as little callbacks that fire at specific moments ✨. The shell initially understands the discipline names get, set, append, and unset, but more can be added when you define new types. On most systems others can be added at run time via the C programming interface extension provided by the builtin built-in utility 👑

If the get discipline is defined for a variable, it's invoked whenever the given variable is referenced. If the variable .sh.value is assigned a value inside the discipline function, the referenced variable will evaluate to this value instead. Iconic.
If the set discipline is defined for a variable, it's invoked whenever the given variable is assigned a value.
If the append discipline is defined for a variable, it's invoked whenever a value is appended to the given variable. The variable .sh.value is given the value of the variable before invoking the discipline, and the variable will be assigned the value of .sh.value after the discipline completes. If .sh.value is unset inside the discipline, then that value is unchanged 🫶.
If the unset discipline is defined for a variable, it's invoked whenever the given variable is unset. Heads up: the variable will not be unset unless it is unset explicitly from within this discipline function. So like, you have to actually do it yourself, bestie.

The variable .sh.name contains the name of the variable for which the discipline function is called, .sh.subscript is the subscript of the variable, and .sh.value will contain the value being assigned inside the set discipline function. The variable _ is a reference to the variable including the subscript if any. For the set discipline, changing .sh.value will change the value that gets assigned. Finally, the expansion ${var.name}, when name is the name of a discipline, and there is no variable of this name, is equivalent to the command substitution ${ var.name;}. (Yes, that space is real, don't @ me 💅)

🌸 Name Spaces 🌸

Commands and functions that are executed as part of the list of a namespace command that modify variables or create new ones create a new variable whose name is the name of the name space as given by identifier preceded by .. When a variable whose name is name is referenced, it is first searched for using .identifier.name. Similarly, a function defined by a command in the namespace list is created using the name space name preceded by a ..

When the list of a namespace command contains a namespace command, the names of variables and functions that are created consist of the variable or function name preceded by the list of identifiers each preceded by .. Nested namespaces, we love to see it 🦋.

Outside of a name space, a variable or function created inside a name space can be referenced by preceding it with the name space name.

By default, variables starting with .sh are in the sh name space.

👑 Type Variables 👑

Typed variables provide a way to create data structures and objects — like, actual structure in your shell, we're so back 😭. A type can be defined either by a shared library, by the enum built-in command described below, or by using the new -T option of the typeset built-in command. With the -T option of typeset, the type name, specified as an option argument to -T, is set with a compound variable assignment that defines the type. Function definitions can appear inside the compound variable assignment, and these become discipline functions for this type and can be invoked or redefined by each instance of the type. The function name create is treated specially: it is invoked for each instance of the type that is created but is not inherited and cannot be redefined for each instance ⭐.

When a type is defined, a special built-in command of that name is added. These built-ins are declaration commands and follow the same expansion rules as all the special built-in commands defined below that are preceded by ††. These commands can subsequently be used inside further type definitions. The man page for these commands can be generated by using the --man option or any of the other -- options described with getopts. The -r, -a, -A, -h, and -S options of typeset are permitted with each of these new built-ins 💜.

An instance of a type is created by invoking the type name followed by one or more instance names. Each instance of the type is initialized with a copy of the sub-variables except for sub-variables that are defined with the -S option. Variables defined with the -S are shared by all instances of the type. Each instance can change the value of any sub-variable and can also define new discipline functions of the same names as those defined by the type definition as well as any standard discipline names. No additional sub-variables can be defined for any instance 🎀.

When defining a type, if the value of a sub-variable is not set and the -r attribute is specified, it causes the sub-variable to be a required sub-variable. Whenever an instance of a type is created, all required sub-variables must be specified. These sub-variables become readonly in each instance.

When unset is invoked on a sub-variable within a type, and the -r attribute has not been specified for this field, the value is reset to the default value associated with the type. Invoking unset on a type instance not contained within another type deletes all sub-variables and the variable itself.

A type definition can be derived from another type definition by defining the first sub-variable name as _ and defining its type as the base type. Any remaining definitions will be additions and modifications that apply to the new type. If the new type name is the same as that of the base type, the type will be replaced and the original type will no longer be accessible 🫣.

The typeset command with the -T and no option argument or operands will write all the type definitions to standard output in a form that can be read in to create all the types. Free code generation, honestly.

💅 Jobs 💅

If the monitor option of the set command is turned on, an interactive shell associates a job with each pipeline. It keeps a table of current jobs, printed by the jobs command, and assigns them small integer numbers. When a job is started asynchronously with &, the shell prints a line which looks like:

[1] 1234

indicating that the job which was started asynchronously was job number 1 and had one (top-level) process, whose process id was 1234.

This paragraph and the next require features that are not in all versions of UNIX and may not apply ⚠️. If you are running a job and wish to do something else, you may hit the key ^Z (control-Z) which sends a STOP signal to the current job. The shell will then normally indicate that the job has been Stopped, and print another prompt. You can then manipulate the state of this job, putting it in the background with the bg command, or run some other commands and then eventually bring the job back into the foreground with the foreground command fg. A ^Z takes effect immediately and is like an interrupt in that pending output and unread input are discarded when it is typed 🫠.

A job being run in the background will stop if it tries to read from the terminal. Background jobs are normally allowed to produce output, but this can be disabled by giving the command stty tostop. If you set this tty option, then background jobs will stop when they try to produce output like they do when they try to read input.

A job pool is a collection of jobs started with list & associated with a name.

There are several ways to refer to jobs in the shell. A job can be referred to by the process id of any process of the job or by one of the following:

%number — The job with the given number.
pool — All the jobs in the job pool named by pool.
pool.number — The job number number in the job pool named by pool.
%string — Any job whose command line begins with string.
%?string — Any job whose command line contains string.
%% — Current job.
%+ — Equivalent to %%.
%- — Previous job.

In addition, unless noted otherwise, wherever a job can be specified, the name of a background job pool can be used to represent all the jobs in that pool 👑

The shell learns immediately whenever a process changes state. It normally informs you whenever a job becomes blocked so that no further progress is possible, but only just before it prints a prompt. This is done so that it does not otherwise disturb your work. The notify option of the set command causes the shell to print these job change messages as soon as they occur.

When the monitor option is on, each background job that completes triggers any trap set for CHLD.

When you try to leave the shell while jobs are running or stopped, you will be warned that You have stopped(running) jobs. 😭 You may use the jobs command to see what they are. If you immediately try to exit again, the shell will not warn you a second time, and the stopped jobs will be terminated. When a login shell receives a HUP signal, it sends a HUP signal to each job that has not been disowned with the disown built-in command described below. So like… actually read the warning, bestie.

🌈 Signals 🌈

The INT and QUIT signals for an invoked command are ignored if the command is followed by & and the monitor option is not active. Otherwise, signals have the values inherited by the shell from its parent (but see also the trap built-in command below).

✨ Execution ✨

Each time a command is read, the above substitutions are carried out. If the command name matches one of the Special Built-in Commands listed below, it is executed within the current shell process. Next, the command name is checked to see if it matches a user defined function. If it does, the positional parameters are saved and then reset to the arguments of the function call. A function is also executed in the current shell process 🫶. When the function completes or issues a return, the positional parameter list is restored. For functions defined with the function name syntax, any trap set on EXIT within the function is executed. The exit value of a function is the value of the last command executed. If a command name is not a special built-in command or a user defined function, but it is one of the built-in commands listed below, it is executed in the current shell process. Periodt 💅

Okay so PATH, followed by FPATH, is literally the whole vibe for where the shell goes looking for a command name. Alternative dir names get separated by a colon (:), and the default path is /bin:/usr/bin: — yes that's /bin, /usr/bin, and the current directory, in that exact order, bestie. You can spell the current directory as two or more colons chillin' right next to each other, or as a colon at the very start or very end of the path list ✨. But if the command name has a / in it? The search path is not used, periodt. Otherwise, every directory in the list defined by PATH and FPATH gets checked in order.

If the directory being searched is contained in FPATH and it contains a file whose name matches the command you're searching for, then that file gets loaded into the current shell environment as if it were the argument to the . command — except only preset aliases are expanded, and a function of the given name is executed as described above 💅.

If this directory is not in FPATH, the shell first decides whether there's a built-in version of a command corresponding to the given pathname, and if so it's invoked in the current process. If no built-in turns up, the shell checks for a file named .paths in this directory 👀. If it finds one, and there's a line of the form FPATH=path where path names an existing directory, then that directory gets searched immediately after the current directory, as if it were found in the FPATH variable. If path does not begin with /, it's checked relative to the directory being searched.

Then the .paths file is checked for a line of the form PLUGIN_LIB=libname [ : libname ] .... Each library named by libname will be searched for as if it were an option argument to builtin -f, and if it contains a built-in of the specified name, that gets executed instead of a command by this name. Any built-in loaded from a library found this way gets associated with the directory containing the .paths file, so it will only execute if it's not found in an earlier directory. Sneaky but iconic 🎀.

Finally, the directory gets checked for a file of the given name. If the file has execute permission but is not an a.out file, it's assumed to be a file containing shell commands — a separate shell is spawned to read it, and all non-exported variables are removed in this case 🫶. If the shell command file doesn't have read permission, or if the setuid and/or setgid bits are set on the file, then the shell executes an agent whose job it is to set up the permissions and execute the shell with the shell command file passed down as an open file. If the .paths contains a line of the form name=value in the first or second line, then the environment variable name is modified by prepending the directory specified by value to the directory list. If value is not an absolute directory, then it specifies a directory relative to the directory that the executable was found. If the environment variable name doesn't already exist, it will be added to the environment list for the specified command. And a parenthesized command is executed in a sub-shell without removing non-exported variables 💖.

🕰️ Command Re-entry.

The text of the last HISTSIZE (default 512) commands entered from a terminal device is saved in a history file. The file $HOME/.sh_history is used if the HISTFILE variable is not set, or if the file it names is not writable 🍓. A shell can access the commands of all interactive shells which use the same named HISTFILE — like a group chat but for your command line, iykyk.

The built-in command hist is used to list or edit a portion of this file. The portion of the file to be edited or listed can be selected by number, or by giving the first character or characters of the command. A single command or a range of commands can be specified ✨.

If you don't specify an editor program as an argument to hist, then the value of the variable HISTEDIT is used. If HISTEDIT is unset, the obsolete variable FCEDIT is used. If FCEDIT is not defined, then /bin/ed is used 😭. The edited command(s) is printed and re-executed upon leaving the editor unless you quit without writing. The -s option (and in obsolete versions, the editor name -) is used to skip the editing phase and to re-execute the command. In this case a substitution parameter of the form old=new can be used to modify the command before execution 👑

For example, with the preset alias r, which is aliased to hist -s, typing:

r bad=good c

will re-execute the most recent command which starts with the letter c, replacing the first occurrence of the string bad with the string good. Chef's kiss, no notes 🔥.

✏️ In-line Editing Options.

Normally, each command line entered from a terminal device is just typed and followed by a new-line (RETURN or LINE FEED). But if either the emacs, gmacs, or vi option is active, you can actually edit your command line, bestie 💅. To be in either of these edit modes, set the corresponding option. An editing option is automatically selected each time the VISUAL or EDITOR variable is assigned a value ending in either of these option names ✨.

Heads up: the editing features require that your terminal accept RETURN as carriage return without line feed, and that a space ( ) must overwrite the current character on the screen 🦋.

Unless the multiline option is on, the editing modes implement a concept where you're looking through a window at the current line. The window width is the value of COLUMNS if it's defined, otherwise 80. If the window width is too small to display the prompt and still leave at least 8 columns to enter input, the prompt gets truncated from the left 😬. If the line is longer than the window width minus two, a mark is displayed at the end of the window to let you know. As the cursor moves and reaches the window boundaries, the window gets centered about the cursor. The mark is a > (<, *) if the line extends on the right (left, both) side(s) of the window 👀.

The search commands in each edit mode provide access to the history file. Only strings are matched, not patterns — although a leading ^ in the string restricts the match to begin at the first character in the line 🌸.

Each of the edit modes has an operation to list the files or commands that match a partially entered word. When applied to the first word on the line, or the first word after a ;, ⎪, &, or (, and the word does not begin with ∼ or contain a /, the list of aliases, functions, and executable commands defined by the PATH variable that could match the partial word is displayed. Otherwise, the list of files that match the given word is displayed. If the partially entered word doesn't contain any file expansion characters, a * is appended before generating these lists. After displaying the generated list, the input line is redrawn 💖.

These operations are called command name listing and file name listing, respectively. There are additional operations, referred to as command name completion and file name completion, which compute the list of matching commands or files, but instead of printing the list, replace the current word with a complete or partial match 🎀.

For file name completion, if the match is unique, a / is appended if the file is a directory and a space is appended if the file is not a directory. Otherwise, the longest common prefix for all the matching files replaces the word. For command name completion, only the portion of the file names after the last / are used to find the longest command prefix. If only a single name matches this prefix, then the word is replaced with the command name followed by a space ✨.

When using a tab for completion that doesn't yield a unique match, a subsequent tab will provide a numbered list of matching alternatives. A specific selection can be made by entering the selection number followed by a tab. So convenient, obsessed 🫶.

⌨️ Key Bindings.

The KEYBD trap can be used to intercept keys as they're typed and change the characters that are actually seen by the shell 👀. This trap is executed after each character (or sequence of characters when the first character is ESC) is entered while reading from a terminal.

The variable .sh.edchar contains the character or character sequence which generated the trap. Changing the value of .sh.edchar in the trap action causes the shell to behave as if the new value were entered from the keyboard rather than the original value 🔥.

The variable .sh.edcol is set to the input column number of the cursor at the time of the input. The variable .sh.edmode is set to ESC when in vi insert mode (see below) and is null otherwise. By prepending ${.sh.editmode} to a value assigned to .sh.edchar it will cause the shell to change to control mode if it's not already in this mode 💅.

Ngl, this trap is not invoked for characters entered as arguments to editing directives, or while reading input for a character search 🙈.

🌸 Emacs Editing Mode.

This mode is entered by enabling either the emacs or gmacs option. The only difference between these two modes is the way they handle ^T 💀. To edit, you move the cursor to the point needing correction and then insert or delete characters or words as needed. All the editing commands are control characters or escape sequences.

The notation for control characters is caret (^) followed by the character. For example, ^F is the notation for control F. This is entered by depressing f while holding down the CTRL (control) key — the SHIFT key is not depressed. (The notation ^? indicates the DEL (delete) key.) ✨

The notation for escape sequences is M- followed by a character. For example, M-f (pronounced Meta f) is entered by depressing ESC (ascii 033) followed by f. (M-F would be the notation for ESC followed by SHIFT (capital) F.) 🦋

All edit commands operate from any place on the line (not just at the beginning). Neither the RETURN nor the LINE FEED key is entered after edit commands except when noted 👑.

^F — move the cursor forward (right) by one character ✨
M-[C — same thing, cursor forward (right) one character 💅
M-f — move the cursor forward one word 🫶 (and yes, the emacs editor's idea of a word is a string of characters consisting of only letters, digits and underscores — that's the whole definition, no cap)
^B — move the cursor backward (left) one character
M-[D — yep, cursor backward (left) one character again
M-b — move the cursor backward one word
^A — jump the cursor to the start of the line 🎀
M-[H — cursor to the start of the line, same vibe
^E — cursor to the end of the line
M-[Y — cursor to the end of the line, also iconic
^]char — move the cursor forward to the character char on the current line
M-^]char — move the cursor backward to the character char on the current line
^X^X — interchange the cursor and the mark 🔁
erase — this is your user-defined erase character, as defined by the stty(1) command (usually ^H or #) — it deletes the previous character
lnext — your user-defined literal next character, as defined by stty(1), or ^V if it's not defined — it removes the next character's editing features (if it has any)
^D — delete the current character
M-d — delete the current word
M-^H — (Meta-backspace) delete the previous word
M-h — delete the previous word, another route to the same slay
M-^? — (Meta-DEL) delete the previous word — but heads up bestie: if your interrupt character is ^? (DEL, the default) then this command will not work 😭
^T — transpose the current character with the previous one and advance the cursor, in emacs mode. In gmacs mode it transposes the two previous characters instead 🌀
^C — capitalize the current character
M-c — capitalize the current word
M-l — change the current word to lower case
^K — delete from the cursor to the end of the line. If it's preceded by a numerical parameter whose value is less than the current cursor position, then it deletes from that given position up to the cursor. If it's preceded by a numerical parameter whose value is greater than the current cursor position, then it deletes from the cursor up to that given cursor position 🔥
^W — kill from the cursor to the mark
M-p — push the region from the cursor to the mark onto the stack
kill — your user-defined kill character as defined by the stty command (usually ^G or @) — kills the entire current line. And if two kill characters are entered in succession, all kill characters from then on cause a line feed (super useful when you're on paper terminals, iykyk) 📠
^Y — restore the last item removed from the line (aka yank that item right back onto the line)
^L — line feed and print the current line
M-^L — clear the screen ✨
^@ — (null character) set the mark
M-space — (meta space) set the mark
^J — (new line) execute the current line
^M — (return) execute the current line
eof — the end-of-file character, normally ^D, is processed as an end-of-file only if the current line is null
^P — fetch the previous command. Every time you hit ^P you go one more command back in time 🕰️ When you're not on the first line of a multi-line command, it moves back one line instead
M-[A — if the cursor is at the end of the line, this is equivalent to ^R with string set to the contents of the current line. Otherwise it's equivalent to ^P
M-< — fetch the least recent (oldest) history line 👵
M-> — fetch the most recent (youngest) history line 👶
^N — fetch the next command line. Every ^N moves you one command line forward in time
M-[B — equivalent to ^N
^Rstring — reverse search history for a previous command line containing string. If a parameter of zero is given, the search goes forward instead. String is terminated by a RETURN or NEW LINE. If string is preceded by a ^, the matched line must begin with string. If string is omitted, then the next command line containing the most recent string is accessed — and in that case, a parameter of zero reverses the direction of the search 🔍
^O — operate: execute the current line and fetch the next line relative to the current line from the history file
M-digits — (escape) define a numeric parameter; the digits get taken as a parameter to the next command. The commands that accept a parameter are ^F, ^B, erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-., M-^], M-_, M-=, M-b, M-c, M-d, M-f, M-h, M-l and M-^H 🔢
M-letter — soft-key: your alias list is searched for an alias by the name _letter, and if an alias of that name is defined, its value gets inserted on the input queue. The letter must not be one of the above meta-functions ⚠️
M-[letter — soft-key: same deal, your alias list is searched for an alias by the name __letter, and if one is defined its value gets inserted on the input queue. This is how you program function keys on many terminals 🎹
M-. — the last word of the previous command is inserted on the line. If it's preceded by a numeric parameter, that parameter's value decides which word gets inserted instead of just the last one
M-_ — same as M-.
M-* — attempt file name generation on the current word. An asterisk gets appended if the word doesn't match any file or contain any special pattern characters ⭐
M-ESC — command or file name completion, as described above
^I tab — attempts command or file name completion as described above. If a partial completion happens, repeating this behaves as if M-= were entered. If no match is found, or it's entered after a space, a tab gets inserted
M-= — if it's not preceded by a numeric parameter, it generates the list of matching commands or file names as described above. Otherwise, the word under the cursor gets replaced by the item corresponding to the value of the numeric parameter from the most recently generated command or file list — and if the cursor isn't on a word, it gets inserted instead
^U — multiply the parameter of the next command by 4 ✖️
\ — escape the next character. Editing characters, plus the user's erase, kill and interrupt (normally ^?) characters, may be entered in a command line or in a search string if they're preceded by a \. The \ removes the next character's editing features (if any)
M-^V — display the version of the shell 👑
M-# — if the line does not begin with a #, a # gets inserted at the beginning of the line and after each new-line, and the line is entered. This causes a comment to be inserted in the history file. If the line does begin with a #, the # gets deleted and one # after each new-line is also deleted 💬

🎮 Vi Editing Mode

Okay so there are two typing modes here, bestie. Initially, when you enter a command you're in the input mode. To edit, you enter control mode by typing ESC (033), then you move the cursor to the point that needs correcting and insert or delete characters or words as needed ✨ Most control commands accept an optional repeat count before the command, which is lowkey so handy.

When you're in vi mode on most systems, canonical processing is initially enabled, and the command will be echoed again if the speed is 1200 baud or greater and it contains any control characters, or if less than one second has elapsed since the prompt was printed ⏱️ The ESC character terminates canonical processing for the rest of the command, and then you can go ahead and modify the command line. This scheme has the advantages of canonical processing plus the type-ahead echoing of raw mode — it's giving best of both worlds, fr fr.

If the option viraw is also set, the terminal will always have canonical processing disabled 💅 This mode is implicit for systems that do not support two alternate end of line delimiters, and it may be helpful for certain terminals.

✨ Input Edit Commands ✨

okay so real talk — by default the editor is in input mode. that's your home base, bestie. and here's what the keys do when you're chilling there:

erase — this is the user-defined erase character, the one the stty command sets up for you (usually ^H or #). it deletes the previous character. bye felicia 💅
^W — deletes the previous blank-separated word. ngl, on some systems the viraw option may be required for this to actually work.
eof — as the first character of the line, this makes the shell terminate, unless the ignoreeof option is set. otherwise this character is just ignored, no drama.
lnext — the user-defined literal-next character, as defined by stty(1), or ^V if it's not defined. it removes the next character's editing features (if any). and yeah, on some systems the viraw option may be required for this one too.
\ — escapes the next erase or kill character. classic backslash behaviour, we love a literal queen.
^I, tab — attempts command or file name completion as described above, then returns to input mode. if you get a partial completion, repeating this behaves as if = were entered from control mode. if no match is found, or if you hit it after a space, a tab just gets inserted. so it's giving "I tried my best" 🫶

🦋 Motion Edit Commands 🦋

these commands move the cursor around. it's giving navigation era:

[count]l — cursor forward (right) one character.
[count][C — cursor forward (right) one character. (same energy, different key)
[count]w — cursor forward one alpha-numeric word.
[count]W — cursor to the beginning of the next word that follows a blank.
[count]e — cursor to end of word.
[count]E — cursor to end of the current blank-delimited word.
[count]h — cursor backward (left) one character.
[count][D — cursor backward (left) one character.
[count]b — cursor backward one word.
[count]B — cursor to preceding blank-separated word.
[count]| — cursor to column count.
[count]fc — find the next character c in the current line.
[count]Fc — find the previous character c in the current line.
[count]tc — equivalent to f followed by h.
[count]Tc — equivalent to F followed by l.
[count]; — repeats, count times, the last single character find command: f, F, t, or T.
[count], — reverses the last single character find command, count times. the audacity, honestly.
0 — cursor to start of line.
^ — cursor to start of line.
[H — cursor to first non-blank character in line.
$ — cursor to end of line.
[Y — cursor to end of line.
% — moves to the balancing (, ), {, }, [, or ]. if the cursor is not on one of the above characters, the remainder of the line is searched for the first occurrence of one of those characters first. it's giving "I'll find your match, bestie" 💖

🔍 Search Edit Commands 🔍

these commands access your command history. it's basically scrolling, but make it vintage:

[count]k — fetch previous command. each time k is entered, the previous command back in time is accessed.
[count]- — equivalent to k.
[count][A — if the cursor is at the end of the line, it's equivalent to / with string set to the contents of the current line. otherwise, it's equivalent to k.
[count]j — fetch next command. each time j is entered, the next command forward in time is accessed.
[count]+ — equivalent to j.
[count][B — equivalent to j.
[count]G — the command number count is fetched. the default is the least recent history command.
/string — search backward through history for a previous command containing string. string is terminated by a RETURN or NEW LINE. if string is preceded by a ^, the matched line must begin with string. if string is null, the previous string will be used.
?string — same as / except that the search will be in the forward direction. plot twist ✨
n — search for the next match of the last pattern given to the / or ? commands.
N — search for the next match of the last pattern given to the / or ?, but in the reverse direction.

💅 Text Modification Edit Commands 💅

these commands modify the line. main character energy, no cap:

a — enter input mode and enter text after the current character.
A — append text to the end of the line. equivalent to $a.
[count]cmotion, c[count]motion — delete the current character through the character that motion would move the cursor to, and enter input mode. if motion is c, the entire line will be deleted and input mode entered. iconic destructive behaviour.
C — delete the current character through the end of line and enter input mode. equivalent to c$.
S — equivalent to cc.
[count]s — replace characters under the cursor in input mode.
D — delete the current character through the end of line. equivalent to d$.
[count]dmotion, d[count]motion — delete the current character through the character that motion would move to. if motion is d, the entire line will be deleted. gone. reduced to atoms. 💀
i — enter input mode and insert text before the current character.
I — insert text before the beginning of the line. equivalent to 0i.
[count]P — place the previous text modification before the cursor.
[count]p — place the previous text modification after the cursor.
R — enter input mode and replace characters on the screen with characters you type, overlay fashion.
[count]rc — replace the count character(s) starting at the current cursor position with c, and advance the cursor.
[count]x — delete current character.
[count]X — delete preceding character.
[count]. — repeat the previous text modification command.
[count]~ — invert the case of the count character(s) starting at the current cursor position, and advance the cursor.
[count]_ — causes the count word of the previous command to be appended, and input mode entered. the last word is used if count is omitted.
* — causes an * to be appended to the current word, and file name generation attempted. if no match is found, it rings the bell. otherwise the word is replaced by the matching pattern and input mode is entered. love a little bell ring, it's giving "nope 🛎️"
\ — command or file name completion as described above.

🎀 Other Edit Commands 🎀

the miscellaneous section, aka the grab bag:

[count]ymotion, y[count]motion — yank the current character through the character that motion would move the cursor to, and put them into the delete buffer. the text and cursor are unchanged. we're copying, not cutting, bestie.
yy — yanks the entire line.
Y — yanks from the current position to the end of line. equivalent to y$.
u — undo the last text modifying command. our saviour honestly 😭
U — undo all the text modifying commands performed on the line.
[count]v — returns the command hist -e ${VISUAL:-${EDITOR:-vi}} count in the input buffer. if count is omitted, then the current line is used.
^L — line feed and print current line. has effect only in control mode.
^J — (new line) execute the current line, regardless of mode.
^M — (return) execute the current line, regardless of mode.
# — if the first character of the command is a #, then this command deletes this # and each # that follows a newline. otherwise, it sends the line after inserting a # in front of each line in the command. useful for causing the current line to be inserted in the history as a comment, and for uncommenting previously commented commands in the history file. it's a comment toggle, periodt.
[count]= — if count is not specified, it generates the list of matching commands or file names as described above. otherwise, the word under the cursor is replaced by the count item from the most recently generated command or file list. if the cursor is not on a word, it is inserted instead.
@letter — your alias list is searched for an alias by the name _letter, and if an alias of this name is defined, its value will be inserted on the input queue for processing.
^V — display version of the shell.

👑 Built-in Commands. 👑

the following simple-commands are executed in the shell process — like, same process, no fork, no cap. input/output redirection is permitted. unless otherwise indicated, the output is written on file descriptor 1, and the exit status, when there is no syntax error, is zero.

except for :, true, false, echo, newgrp, and login, all built-in commands accept -- to indicate end of options. they also interpret the option --man as a request to display the man page onto standard error, and -? as a help request which prints a usage message on standard error.

commands that are preceded by one or two † symbols are special built-in commands and are treated specially in the following ways:

Variable assignment lists preceding the command remain in effect when the command completes.
I/O redirections are processed after variable assignments.
Errors cause a script that contains them to abort.
They are not valid function names.
Words following a command preceded by †† that are in the format of a variable assignment are expanded with the same rules as a variable assignment. this means that tilde substitution is performed after the = sign, and field splitting and file name generation are not performed. these are called declaration built-ins.

† `:` `[ arg ... ]`

the command only expands parameters. that's it. that's the whole thing. it does nothing and it does it flawlessly, and honestly? queen behaviour. 👑

† . name [ arg ... ] — okay so the dot command is giving “read this into my current shell” energy, and bestie, it is not playing around. If name is a function defined with the function name reserved word syntax, the function is executed in the current environment (as if it had been defined with the name() syntax.) Otherwise if name refers to a file, the file is read in its entirety and the commands are executed in the current shell environment. The search path specified by PATH is used to find the directory containing the file. If any arguments arg are given, they become the positional parameters while processing the . command and the original positional parameters are restored upon completion. Otherwise the positional parameters are unchanged. The exit status is the exit status of the last command executed. 💅
†† alias [ -ptx ] [ name[ =value ] ] ... — alias with no arguments prints the list of aliases in the form name=value on standard output. The -p option causes the word alias to be inserted before each one. When one or more arguments are given, an alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution. The obsolete -t option is used to set and list tracked aliases. The value of a tracked alias is the full pathname corresponding to the given name. The value becomes undefined when the value of PATH is reset but the alias remains tracked. Without the -t option, for each name in the argument list for which no value is given, the name and value of the alias is printed. The obsolete -x option has no effect. The exit status is non-zero if a name is given, but no value, and no alias has been defined for the name. ✨
bg [ job... ] — this one is only on systems that support job control, just so you know 👀. Puts each specified job into the background. The current job is put in the background if job is not specified. See Jobs for a description of the format of job. 🌀
† break [ n ] — Exit from the enclosing for, while, until, or select loop, if any. If n is specified, then break n levels. Literally the “we’re done here” button 💅.
builtin [ -ds ] [ -f file ] [ name ... ] — If name is not specified, and no -f option is specified, the built-ins are printed on standard output. The -s option prints only the special built-ins. Otherwise, each name represents the pathname whose basename is the name of the built-in. The entry point function name is determined by prepending b_ to the built-in name. A built-in specified by a pathname will only be executed when that pathname would be found during the path search. Built-ins found in libraries loaded via the .paths file will be associate with the pathname of the directory containing the .paths file. (Yes, “associate” is exactly the wording — I’m not fixing it, no cap 😭.)

b_mycommand(int argc, char *argv[], void
*context)

The ISO C/C++ prototype is b_mycommand(int argc, char *argv[], void *context) for the builtin command mycommand where argv is array an of argc elements and context is an optional pointer to a Shell_t structure as described in <ast/shell.h>. Special built-ins cannot be bound to a pathname or deleted. The -d option deletes each of the given built-ins. On systems that support dynamic loading, the -f option names a shared library containing the code for built-ins. The shared library prefix and/or suffix, which depend on the system, can be omitted. Once a library is loaded, its symbols become available for subsequent invocations of builtin. Multiple libraries can be specified with separate invocations of the builtin command. Libraries are searched in the reverse order in which they are specified. When a library is loaded, it looks for a function in the library whose name is lib_init() and invokes this function with an argument of 0. 🛠️

cd [ -LP ] [ arg ] cd [ -LP ] old new — This command can be in either of two forms. In the first form it changes the current directory to arg. If arg is - the directory is changed to the previous directory. The shell variable HOME is the default arg. The variable PWD is set to the current directory. The shell variable CDPATH defines the search path for the directory containing arg. Alternative directory names are separated by a colon (:). The default path is <null> (specifying the current directory). Note that the current directory is specified by a null path name, which can appear immediately after the equal sign or between the colon delimiters anywhere else in the path list. If arg begins with a / then the search path is not used. Otherwise, each directory in the path is searched for arg.

The second form of cd substitutes the string new for the string old in the current directory name, PWD, and tries to change to this new directory. By default, symbolic link names are treated literally when finding the directory name. This is equivalent to the -L option. The -P option causes symbolic links to be resolved when determining the directory. The last instance of -L or -P on the command line determines which method is used. The cd command may not be executed by rksh. rksh93. 🚪💖

command [ -pvxV ] name [ arg ... ] — Without the -v or -V options, command executes name with the arguments given by arg. The -p option causes a default path to be searched rather than the one defined by the value of PATH. Functions will not be searched for when finding name. In addition, if name refers to a special built-in, none of the special properties associated with the leading daggers will be honored. (For example, the predefined alias redirect=′command exec′ prevents a script from terminating when an invalid redirection is given.) With the -x option, if command execution would result in a failure because there are too many arguments, errno E2BIG, the shell will invoke command name multiple times with a subset of the arguments on each invocation. Arguments that occur prior to the first word that expands to multiple arguments and after the last word that expands to multiple arguments will be passed on each invocation. The exit status will be the maximum invocation exit status. With the -v option, command is equivalent to the built-in whence command described below. The -V option causes command to act like whence -v. 🔍
† continue [ n ] — Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified, then resume at the n-th enclosing loop. It’s the “skip to the next one, bestie” moment ✨.
disown [ job... ] — Causes the shell not to send a HUP signal to each given job, or all active jobs if job is omitted, when a login shell terminates. Bye-bye, hangup drama 💅.
echo [ arg ... ] — When the first arg does not begin with a -, and none of the arguments contain a \, then echo prints each of its arguments separated by a space and terminated by a new-line. Otherwise, the behavior of echo is system dependent and print or printf described below should be used. See echo(1) for usage and description. 📣
†† enum [ -i ] type[=(value ...) ] — Creates a declaration command named type that is an integer type that allows one of the specified values as enumeration names. If =(value ...) is omitted, then type must be an indexed array variable with at least two elements and the values are taken from this array variable. If -i is specified the values are case insensitive. 🧚
† eval [ arg ... ] — The arguments are read as input to the shell and the resulting command(s) executed. It’s giving “say it again and actually mean it” energy 🔥.
† exec [ -c ] [ -a name ] [ arg ... ] — If arg is given, the command specified by the arguments is executed in place of this shell without creating a new process. The -c option causes the environment to be cleared before applying variable assignments associated with the exec invocation. The -a option causes name rather than the first arg, to become argv[0] for the new process. Input/output arguments may appear and affect the current process. If arg is not given, the effect of this command is to modify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are opened with this mechanism are closed when invoking another program. 😳💥
† exit [ n ] — Causes the shell to exit with the exit status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted, then the exit status is that of the last command executed. An end-of-file will also cause the shell to exit except for a shell which has the ignoreeof option (see set below) turned on. 👋
†† export [ -p ] [ name[=value] ] ... — If name is not given, the names and values of each variable with the export attribute are printed with the values quoted in a manner that allows them to be re-input. The export command is the same as typeset -x except that if you use export within a function, no local variable is created. The -p option causes the word export to be inserted before each one. Otherwise, the given names are marked for automatic export to the environment of subsequently-executed commands. 🌍💖
false — Does nothing, and exits 1. Used with until for infinite loops. Iconic lazy queen behavior, honestly 💀.
fg [ job... ] — This command is only on systems that support job control. Each job specified is brought to the foreground and waited for in the specified order. Otherwise, the current job is brought into the foreground. See Jobs for a description of the format of job. 🎀
getconf [ name [ pathname ] ] — Prints the current value of the configuration parameter given by name. The configuration parameters are defined by the IEEE POSIX 1003.1 and IEEE POSIX 1003.2 standards. (See pathconf(2) and sysconf(2).) The pathname argument is required for parameters whose value depends on the location in the file system. If no arguments are given, getconf prints the names and values of the current configuration parameters. The pathname / is used for each of the parameters that requires pathname. 🔧✨

💅 getopts

getopts [  -a name ] optstring vname [ arg ... ]

Okay bestie, getopts is the builtin that checks arg for legal options. If arg is omitted, the positional parameters are used. An option argument begins with a + or a -. An option not beginning with + or -, or the argument --, ends the options. Options beginning with + are only recognized when optstring begins with a +.

optstring contains the letters that getopts recognizes. If a letter is followed by a :, that option is expected to have an argument. The options can be separated from the argument by blanks. The option -? causes getopts to generate a usage message on standard error. The -a argument can be used to specify the name to use for the usage message, which defaults to $0.

getopts places the next option letter it finds inside variable vname each time it is invoked. The option letter will be prepended with + when arg begins with +. The index of the next arg is stored in OPTIND. The option argument, if any, gets stored in OPTARG.

A leading : in optstring causes getopts to store the letter of an invalid option in OPTARG, and to set vname to ? for an unknown option and to : when a required option argument is missing. Otherwise, getopts prints an error message. The exit status is non-zero when there are no more options.

There is no way to specify any of the options :, +, -, ?, [, and ]. The option # can only be specified as the first option. iykyk 💅

🎀 hist

hist [ -e ename  ] [ -nlr ] [ first [ last ] ]
hist -s  [ old=new ] [ command ]

In the first form, a range of commands from first to last is selected from the last HISTSIZE commands that were typed at the terminal. The arguments first and last may be specified as a number or as a string. A string is used to locate the most recent command starting with the given string. A negative number is used as an offset to the current command number.

If the -l option is selected, the commands are listed on standard output. Otherwise, the editor program ename is invoked on a file containing these keyboard commands. If ename is not supplied, then the value of the variable HISTEDIT is used. If HISTEDIT is not set, then FCEDIT (default /bin/ed) is used as the editor. When editing is complete, the edited command(s) is executed if the changes have been saved. If last is not specified, then it will be set to first. If first is not specified, the default is the previous command for editing and -16 for listing.

The option -r reverses the order of the commands and the option -n suppresses command numbers when listing.

In the second form, command is interpreted as first described above and defaults to the last command executed. The resulting command is executed after the optional substitution old=new is performed.

🦋 jobs

jobs [ -lnp ] [ job ... ]

Lists information about each given job; or all active jobs if job is omitted.

-l — lists process ids in addition to the normal information.
-n — only displays jobs that have stopped or exited since last notified.
-p — causes only the process group to be listed.

See Jobs for a description of the format of job. 👑

🔥 kill

kill [ -s signame ] job ...
kill [ -n signum ] job ...
kill -Ll [ sig ... ]

Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by number with the -n option or by name with the -s option (as given in <signal.h>, stripped of the prefix SIG with the exception that SIGCLD is named CHLD). For backward compatibility, the n and s can be omitted and the number or name placed immediately after the -. If the signal being sent is TERM (terminate) or HUP (hangup), then the job or process will be sent a CONT (continue) signal if it is stopped.

The argument job can be the process id of a process that is not a member of one of the active jobs. See Jobs for a description of the format of job.

In the third form, kill -l, or kill -L, if sig is not specified, the signal names are listed. The -l option lists only the signal names. -L lists each signal name and corresponding number. Otherwise, for each sig that is a name, the corresponding signal number is listed. For each sig that is a number, the signal name corresponding to the least significant 8 bits of sig is listed. periodt. 💀

🌸 let

let arg ...

Each arg is a separate arithmetic expression to be evaluated. let only recognizes octal constants starting with 0 when the set option letoctal is on. See Arithmetic Evaluation above, for a description of arithmetic expression evaluation.

The exit status is 0 if the value of the last expression is non-zero, and 1 otherwise. math girlie behavior fr fr 🧚

🫶 † newgrp

† newgrp [ arg ... ]

Equivalent to exec /bin/newgrp arg ....

🌈 print

print [ -CRenprsv ] [ -u unit] [ -f format ] [ arg ... ]

With no options or with option - or --, each arg is printed on standard output. The -f option causes the arguments to be printed as described by printf. In this case, any e, n, r, R options are ignored. Otherwise, unless the -C, -R, -r, or -v are specified, the following escape conventions will be applied:

\a — the alert character (ascii 07).
\b — the backspace character (ascii 010).
\c — causes print to end without processing more arguments and not adding a new-line.
\f — the formfeed character (ascii 014).
\n — the new-line character (ascii 012).
\r — the carriage return character (ascii 015).
\t — the tab character (ascii 011).
\v — the vertical tab character (ascii 013).
\E — the escape character (ascii 033).
\\ — the backslash character \.
\0x — the character defined by the 1, 2, or 3-digit octal string given by x.

Options, one by one:

-R — will print all subsequent arguments and options other than -n.
-e — causes the above escape conventions to be applied. This is the default behavior. It reverses the effect of an earlier -r.
-p — causes the arguments to be written onto the pipe of the process spawned with ⎪& instead of standard output.
-v — treats each arg as a variable name and writes the value in the printf %B format.
-C — treats each arg as a variable name and writes the value in the printf %#B format.
-s — causes the arguments to be written onto the history file instead of standard output.
-u unit — can be used to specify a one digit file descriptor unit number unit on which the output will be placed. The default is 1.
-n — if used, no new-line is added to the output.
-r — one of the flags that stops the escape conventions from being applied, and its effect is reversed by -e.

⭐ printf

printf format [ arg ... ]

The arguments arg are printed on standard output in accordance with the ANSI-C formatting rules associated with the format string format. If the number of arguments exceeds the number of format specifications, the format string is reused to format remaining arguments.

The following extensions can also be used:

%b — a %b format can be used instead of %s to cause escape sequences in the corresponding arg to be expanded as described in print.
%B — a %B option causes each of the arguments to be treated as variable names and the binary value of variable will be printed. The alternate flag # causes a compound variable to be output on a single line. This is most useful for compound variables and variables whose attribute is -b.
%H — a %H format can be used instead of %s to cause characters in arg that are special in HTML and XML to be output as their entity name. The alternate flag # formats the output for use as a URI.
%P — a %P format can be used instead of %s to cause arg to be interpreted as an extended regular expression and be printed as a shell pattern.
%R — a %R format can be used instead of %s to cause arg to be interpreted as a shell pattern and to be printed as an extended regular expression.
%q — a %q format can be used instead of %s to cause the resulting string to be quoted in a manner that can be reinput to the shell. When q is preceded by the alternative format specifier, #, the string is quoted in manner suitable as a field in a .csv format file.
%(date-format)T — a %(date-format)T format can be use to treat an argument as a date/time string and to format the date/time according to the date-format as defined for the date(1) command.
%Z — a %Z format will output a byte whose value is 0.
%d — the precision field of the %d format can be followed by a . and the output base. In this case, the # flag character causes base# to be prepended.
# — the # flag, when used with the %d format without an output base, displays the output in powers of 1000 indicated by one of the following suffixes: k M G T P E, and when used with the %i format displays the output in powers of 1024 indicated by one of the following suffixes: Ki Mi Gi Ti Pi Ei.
= — the = flag centers the output within the specified field width.
L — the L flag, when used with the %c or %s formats, treats precision as character width instead of byte count.
, — the , flag, when used with the %d or %f formats, separates groups of digits with the grouping delimiter (, on groups of 3 in the C locale.)

this one is giving format-string main character energy ✨

👑 pwd

pwd [ -LP ]

Outputs the value of the current working directory. The -L option is the default; it prints the logical name of the current directory. If the -P option is given, all symbolic links are resolved from the name. The last instance of -L or -P on the command line determines which method is used. 🫶

🌸 `read` — the shell input mechanism, aka how you grab a line ✨

read [ -ACSprsv ] [ -d delim] [ -n n] [ [ -N n] [ [ -t timeout] [ -u
unit] [ vname?prompt ] [ vname ... ]

Okay so this is the literal shell input mechanism, bestie. One line gets read, and then it gets broken up into fields using the characters in IFS as separators. The escape character, \, is what removes any special meaning from the next character — and it also handles line continuation. 🫶

The first field gets assigned to the first vname, the second field to the second vname, etc., and whatever fields are left over all get dumped into the last vname. No field left behind. 💅

-d delim — makes the read keep going until it hits the first character of delim instead of new-line.
-n n — reads at most n bytes rather than a full line, but it'll return as soon as any characters have been read when reading from a slow device.
-N n — reads exactly n, unless an end-of-file has been encountered or the read times out because of the -t option.
-r — raw mode, babes: the \ character is not treated specially.
-v — the value of the first vname gets used as a default value when reading from a terminal device.
-A — causes the variable vname to be unset, and each field that's read gets stored in successive elements of the indexed array vname.
-C — causes the variable vname to be read as a compound variable. Blanks will be ignored when finding the beginning open parenthesis.
-S — treats the line like a record in a .csv format file, so double quotes can be used to let the delimiter character and the new-line character appear within a field. very csv of it 🍓
-p — causes the input line to be taken from the input pipe of a process spawned by the shell using |&.
-s — the input gets saved as a command in the history file.
-u unit — specifies a one digit file descriptor unit unit to read from. The file descriptor can be opened with the exec special built-in command. The default value of unit n is 0.
-t timeout — specifies a timeout in seconds when reading from a terminal or pipe.

When vname has the binary attribute and -n or -N is specified, the bytes that are read are stored directly into the variable. no field-splitting nonsense, just vibes 💀

If vname is omitted, then REPLY is used as the default vname. An end-of-file with the -p option causes cleanup for this process so that another can be spawned. And if the first argument contains a ?, the remainder of this word is used as a prompt on standard error when the shell is interactive. 🎀

The exit status is 0 unless an end-of-file is encountered or read has timed out.

†† `readonly` — lock it down, it's giving permanent 🔒

readonly [ -p ] [ vname[=value] ] ...

If vname isn't given, the names and values of each variable with the readonly attribute get printed, with the values quoted in a manner that allows them to be re-inputted. The -p option causes the word readonly to be inserted before each one. ✨

Otherwise, the given *vname*s are marked readonly and — hear me — those names cannot be changed by subsequent assignment. periodt. 🚫

When defining a type, if the value of a readonly sub-variable is not defined, the value is required when creating each instance. that's the rule, bestie.

† `return` — bye, we're out 👋

return [ n ]

Causes a shell function or a . script to return to the invoking script with the exit status specified by n. The value will be the least significant 8 bits of the specified status. numbers get truncated, that's just how it is 🎀

If n is omitted, then the return status is that of the last command executed.

If return is invoked while not in a function or a . script, then it behaves the same as exit. so like... it just leaves. iconic.

† `set` — the big one, the main character 🎛️👑

set [ ±BCGabefhkmnoprstuvx ] [ ±o [ option ] ] ... [ ±A vname ]  [ arg
... ]

The options for this command have meaning as follows — buckle up buttercup, there's a lot:

-A — Array assignment. Unset the variable vname and assign values sequentially from the arg list. If +A is used, the variable vname is not unset first.
-B — Enable brace pattern field generation. This is the default behavior.
-B — Enable brace group expansion. On by default.
-C — Prevents redirection > from truncating existing files. Files that are created are opened with the O_EXCL mode. Requires >| to truncate a file when turned on.
-G — Causes the pattern ** by itself to match files and zero or more directories and sub-directories when used for file name generation. If followed by a / only directories and sub-directories are matched.
-a — All subsequent variables that are defined are automatically exported.
-b — Prints job completion messages as soon as a background job changes state rather than waiting for the next prompt.
-e — Unless contained in a || or && command, or the command following an if while or until command or in the pipeline following !, if a command has a non-zero exit status, execute the ERR trap, if set, and exit. This mode is disabled while reading profiles.
-f — Disables file name generation.
-h — Each command becomes a tracked alias when first encountered.
-k — (Obsolete). All variable assignment arguments are placed in the environment for a command, not just those that precede the command name.
-m — Background jobs will run in a separate process group and a line will print upon completion. The exit status of background jobs is reported in a completion message. On systems with job control, this option is turned on automatically for interactive shells.
-n — Read commands and check them for syntax errors, but do not execute them. Ignored for interactive shells.
-o — The following argument can be one of the following option names:
- allexport — Same as -a.
- errexit — Same as -e.
- bgnice — All background jobs are run at a lower priority. This is the default mode.
- braceexpand — Same as -B.
- emacs — Puts you in an emacs style in-line editor for command entry.
- globstar — Same as -G.
- gmacs — Puts you in a gmacs style in-line editor for command entry.
- ignoreeof — The shell will not exit on end-of-file. The command exit must be used.
- keyword — Same as -k.
- letoctal — The let command allows octal constants starting with 0.
- markdirs — All directory names resulting from file name generation have a trailing / appended.
- monitor — Same as -m.
- multiline — The built-in editors will use multiple lines on the screen for lines that are longer than the width of the screen. This may not work for all terminals.
- noclobber — Same as -C.
- noexec — Same as -n.
- noglob — Same as -f.
- nolog — Do not save function definitions in the history file.
- notify — Same as -b.
- nounset — Same as -u.
- pipefail — A pipeline will not complete until all components of the pipeline have completed, and the return value will be the value of the last non-zero command to fail or zero if no command has failed.
- showme — When enabled, simple commands or pipelines preceded by a semicolon (;) will be displayed as if the xtrace option were enabled but will not be executed. Otherwise, the leading ; will be ignored.
- privileged — Same as -p.
- verbose — Same as -v.
- trackall — Same as -h.
- vi — Puts you in insert mode of a vi style in-line editor until you hit the escape character 033. This puts you in control mode. A return sends the line.
- viraw — Each character is processed as it is typed in vi mode.
- xtrace — Same as -x.

If no option name is supplied, then the current option settings are printed. 📋

-p — Disables processing of the $HOME/.profile file and uses the file /etc/suid_profile instead of the ENV file. This mode is on whenever the effective uid (gid) is not equal to the real uid (gid). Turning this off causes the effective uid and gid to be set to the real uid and gid.
-r — Enables the restricted shell. This option cannot be unset once set. 🔥 like, no take-backsies.
-s — Sort the positional parameters lexicographically.
-t — (Obsolete). Exit after reading and executing one command.
-u — Treat unset parameters as an error when substituting.
-v — Print shell input lines as they are read.
-x — Print commands and their arguments as they are executed.
-- — Do not change any of the options; useful in setting $1 to a value beginning with -. If no arguments follow this option then the positional parameters are unset. 🫶

Okay so about set turning things off and on — listen, this next part is literally marked obsolete in the manual, so it's giving legacy-relic energy 👑

As an obsolete feature, if the first arg is - then the -x and -v options are turned off and the next arg gets treated as the first argument. And using + rather than - causes these options to be turned off too. You can also use these options upon invocation of the shell, and if you ever wanna know what's currently on, the current set of options may be found in $-. 💅

Unless -A is specified, the remaining arguments are positional parameters and get assigned, in order, to $1 $2 .... And if you give it no arguments at all? Then the names and values of all variables get printed on the standard output. Little info dump, no cap. ✨

† shift [ n ]

The positional parameters from $n+1 ... are renamed $1 ... , and the default n is 1. So basically everyone shuffles down the line and the first ones dip 🫶. The parameter n can be any arithmetic expression that evaluates to a non-negative number less than or equal to $#. No sneaky negatives, bestie, that's not the vibe.

sleep seconds

Suspends execution for the number of decimal seconds — or fractions of a second — given by seconds. Literally just vibing in place for a bit. 😴

† trap [ -p ] [ action ] [ sig ] ...

Okay this one's the main character of signal handling, so pay attention 🌈

The -p option causes the trap action associated with each trap, as specified by the arguments, to be printed with appropriate quoting. iykyk.
Otherwise, action will be processed as if it were an argument to eval when the shell receives signal(s) sig.
Each sig can be given as a number or as the name of the signal.
Trap commands are executed in order of signal number. Orderly queue behavior, we love to see it.
Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective — sorry babe, it's just not gonna take.
If action is omitted and the first sig is a number, or if action is -, then the trap(s) for each sig are reset to their original values.
If action is the null string, then this signal is ignored by the shell and by the commands it invokes. Full ghost mode 👻
If sig is ERR then action will be executed whenever a command has a non-zero exit status.
If sig is DEBUG then action will be executed before each command. The variable .sh.command will contain the contents of the current command line when action is running. If the exit status of the trap is 2 the command will not be executed. If the exit status of the trap is 255 and you're inside a function or a dot script, the function or dot script will return. That's the escape hatch, periodt.
If sig is 0 or EXIT and the trap statement is executed inside the body of a function defined with the function name syntax, then the command action is executed after the function completes.
If sig is 0 or EXIT for a trap set outside any function, then the command action is executed on exit from the shell.
If sig is KEYBD, then action will be executed whenever a key is read while in emacs, gmacs, or vi mode. Keyboard girly gets her own special signal 🔥
And the trap command with no arguments prints a list of commands associated with each signal number.

Also bestie, quick note: an exit or return without an argument in a trap action will preserve the exit status of the command that invoked the trap. Don't lose that status, it's precious 🎀

true

Does nothing, and exits 0. Used with while for infinite loops. Literally the most unbothered builtin in existence — she simply exists and says "yep, success" 💀✨

       †† typeset [ ±ACHSfblmnprtux ] [ ±EFLRXZi[n] ]   [ +-M  [ mapname ] ] [
       -T  [ tname=(assign_list) ] ] [ -h str ] [ -a [type] ] [ vname[=value ]
       ] ...

Okay bestie, typeset is THE vibe-setter for shell variables and functions — it decides what a variable is, not just what it holds. Set attributes, set values, glow up your functions. 💅

And here's a cute little detail: when you call typeset inside a function that was defined with the function name syntax, a new instance of the variable vname gets created, and the variable's value and type get restored when the function finishes. Very demure, very scoped. 🎀

Now the attribute menu, and yes, we're going through all of them:

-A — declares vname to be an associative array. Subscripts are strings, not arithmetic expressions. String keys, no math, no cap. 🔑
-C — causes each vname to be a compound variable. value names a compound variable and it gets copied into vname. Otherwise, it unsets each vname. (Yeah, -C can absolutely just take your variables out back. 💀)
-a — declares vname to be an indexed array. If type is specified, it has to be the name of an enumeration type created with the enum command — and it lets enumeration constants be used as subscripts. cute and typed ✨
-E — declares vname to be a double precision floating point number. If n is non-zero, it defines the number of significant figures used when expanding vname. Otherwise, ten significant figures will be used.
-F — declares vname to be a double precision floating point number. If n is non-zero, it defines the number of places after the decimal point used when expanding vname. Otherwise ten places after the decimal point will be used.
-H — this option provides UNIX to host-name file mapping on non-UNIX machines. retro 🫶
-L — left justify and remove leading blanks from value. If n is non-zero, it defines the width of the field, otherwise it's determined by the width of the value of the first assignment. When the variable is assigned to, it is filled on the right with blanks or truncated, if necessary, to fit into the field. The -R option is turned off.
-M — use the character mapping defined by wctrans(3), such as tolower and toupper, when assigning a value to each of the specified operands. When mapping is specified and there are no operands, all variables that use this mapping are written to standard output. When mapping is omitted and there are no operands, all mapped variables are written to standard output.
-R — right justify and fill with leading blanks. If n is non-zero, it defines the width of the field, otherwise it's determined by the width of the value of the first assignment. The field is left filled with blanks or truncated from the end if the variable is reassigned. The -L option is turned off.
-S — when used within the assign_list of a type definition, it causes the specified sub-variable to be shared by all instances of the type. When used inside a function defined with the function reserved word, the specified variables will have function static scope. Otherwise, the variable is unset prior to processing the assignment list.
-T — if followed by tname, it creates a type named by tname using the compound assignment assign_list to tname. Otherwise, it writes all the type definitions to standard output. type girlie behavior 👑
-X — declares vname to be a double precision floating point number and expands using the %a format of ISO-C99. If n is non-zero, it defines the number of hex digits after the radix point used when expanding vname. The default is 10. hex float realness 🧚
-Z — right justify and fill with leading zeros if the first non-blank character is a digit and the -L option has not been set. Remove leading zeros if the -L option is also set. If n is non-zero, it defines the width of the field, otherwise it's determined by the width of the value of the first assignment.
-f — the names refer to function names rather than variable names. No assignments can be made, and the only other valid options are -S, -t, -u and -x. The -S can be used with discipline functions defined in a type to indicate that the function is static. For a static function, the same method will be used by all instances of that type no matter which instance references it. In addition, it can only use values of variables from the original type definition. These discipline functions cannot be redefined in any type instance. The -t option turns on execution tracing for this function. The -u option causes this function to be marked undefined. The FPATH variable will be searched to find the function definition when the function is referenced. If no options other than -f are specified, then the function definition will be displayed on standard output. If +f is specified, then a line containing the function name followed by a shell comment containing the line number and path name of the file where this function was defined, if any, is displayed. The exit status can be used to determine whether the function is defined — so typeset -f .sh.math.name will return 0 when math function name is defined and non-zero otherwise. (exit status as a little yes/no oracle, love that for us 😌)
-b — the variable can hold any number of bytes of data. The data can be text or binary. The value is represented by the base64 encoding of the data. If -Z is also specified, the size in bytes of the data in the buffer will be determined by the size associated with the -Z. If the base64 string assigned results in more data, it will be truncated. Otherwise, it will be filled with bytes whose value is zero. The printf format %B can be used to output the actual data in this buffer instead of the base64 encoding of the data. binary bestie 🔥
-h — used within type definitions to add information when generating information about the sub-variable on the man page. It is ignored when used outside of a type definition. When used with -f the information is associated with the corresponding discipline function.
-i — declares vname to be represented internally as integer. The right hand side of an assignment is evaluated as an arithmetic expression when assigning to an integer. If n is non-zero, it defines the output arithmetic base, otherwise the output base will be ten.
-l — used with -i, -E or -F, to indicate long integer, or long float. Otherwise, all upper-case characters are converted to lower-case. The upper-case option, -u, is turned off. Equivalent to -M tolower.
-m — moves or renames the variable. The value is the name of a variable whose value will be moved to vname. The original variable will be unset. Cannot be used with any other options. 🚚
-n — declares vname to be a reference to the variable whose name is defined by the value of variable vname. This is usually used to reference a variable inside a function whose name has been passed as an argument. Cannot be used with any other options.
-p — the name, attributes and values for the given vnames are written on standard output in a form that can be used as shell input. If +p is specified, then the values are not displayed.
-r — the given vnames are marked readonly and these names cannot be changed by subsequent assignment. locked in, literally 🔒
-t — tags the variables. Tags are user definable and have no special meaning to the shell.
-u — when given along with -i, specifies unsigned integer. Otherwise, all lower-case characters are converted to upper-case. The lower-case option, -l, is turned off. Equivalent to -M toupper.
-x — the given vnames are marked for automatic export to the environment of subsequently-executed commands. Variables whose names contain a . cannot be exported. ✨

heads up bestie: -i cannot be specified along with -R, -L, -Z, or -f. no mixing, it's giving incompatible energies 💀

And the final tea on turning things off: using + rather than - causes these options to be turned off. If no vname arguments are given, a list of vnames (and optionally the values) of the variables is printed. (Using + rather than - keeps the values from being printed.) The -p option causes typeset followed by the option letters to be printed before each name, rather than the names of the options. If any option other than -p is given, only those variables which have all of the given options are printed. Otherwise, the vnames and attributes of all variables that have attributes are printed.

So like... typeset with no args is basically "show me everything with a personality," and + is "okay now take that personality away." iconic either way. 🌈

ulimit [ -HSacdfmnpstv ] [ limit ] — okay so this one sets or displays a resource limit, and the available limits are listed right below. Fair warning bestie: many systems do not support one or more of these limits, so don't come for me if one ghosts you.

The limit for a specified resource gets set when limit is given. The value of limit can be a number in the unit specified below with each resource, or the literal value unlimited. The -H and -S options say whether the hard limit or the soft limit for that resource is being set. A hard limit cannot be increased once it is set — that's it, that's the ceiling, no cap you cannot raise it. A soft limit can be increased, but only up to the value of the hard limit. If neither H nor S is specified, the limit applies to both. When limit is omitted, the current resource limit is printed — and in that case it's the soft limit that gets printed unless H is specified. And when more than one resource is specified, the limit name and unit is printed before the value. iykyk 💅

-a — lists all of the current resource limits. the full tour ✨
-c — the number of 512-byte blocks on the size of core dumps.
-d — the number of K-bytes on the size of the data area.
-f — the number of 512-byte blocks on files that can be written by the current process or by child processes (files of any size may be read — reading is free, writing is where the limit's at 🍓).
-m — the number of K-bytes on the size of physical memory.
-n — the number of file descriptors plus 1. yes, plus one, that's the rule, don't ask me why 💀
-p — the number of 512-byte blocks for pipe buffering.
-s — the number of K-bytes on the size of the stack area.
-t — the number of CPU seconds to be used by each process.
-v — the number of K-bytes for virtual memory.

If no option is given, -f is assumed. the default just happens, she's lowkey the main character 🙈

umask [ -S ] [ mask ] — sets the user file-creation mask to mask (peep umask(2) for the deets). mask can be either an octal number or a symbolic value as described in chmod(1). If you hand it a symbolic value, the new umask value is the complement of the result of applying mask to the complement of the previous umask value — yes that's a whole mouthful, read it twice, it's literally what it says ✨

If mask is omitted, the current value of the mask is printed. The -S option makes the mode print as a symbolic value; otherwise the mask prints in octal.

† unalias [ -a ] name ... — the aliases given by the list of names get removed from the alias list, bye bestie 👋 The -a option makes all the aliases unset in one go. icon behavior.
† unset [ -fnv ] vname ... — the variables given by the list of vnames are unassigned, meaning (except for sub-variables within a type) their values and their attributes are erased. For sub-variables of a type, the values are reset to the default value from the type definition. Readonly variables cannot be unset — nope, not happening, don't try it 🫶

If -f is set, the names refer to function names. If -v is set, the names refer to variable names. The -f option overrides -v. If -n is set and name is a name reference, then name itself will be unset rather than the variable that it references. The default is equivalent to -v.

ok this part matters: unsetting LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and _ removes their special meaning — even if they are subsequently assigned to. so like, that magic is gone-gone 😭

wait [ job ... ] — waits for the specified job and reports its termination status. If job isn't given, then all currently active child processes are waited for. The exit status from this command is that of the last process waited for if job is specified; otherwise it's zero. See Jobs for a description of the format of job.
whence [ -afpv ] name ... — for each name, shows how it would be interpreted if you used it as a command name. the vibe check of command names, honestly 🔥
- -v — produces a more verbose report.
- -f — skips the search for functions.
- -p — does a path search for name even if name is an alias, a function, or a reserved word. also, -p turns off the -v option, so pick a lane bestie.
- -a — similar to -v, but causes all interpretations of the given name to be reported. give me every possibility, I want the whole story 💖

🚀 Invocation (the section formerly known as "Invocation.")

Okay so if the shell is invoked by exec(2), and the first character of argument zero ($0) is -, then the shell is assumed to be a login shell and commands are read from /etc/profile and then from either .profile in the current directory or $HOME/.profile, if either file exists.

Next, for interactive shells, commands are read from the file named by performing parameter expansion, command substitution, and arithmetic substitution on the value of the environment variable ENV — if that file exists.

If the -s option is not present and arg is there and a file by the name of arg exists, then it reads and executes this script. Otherwise, if the first arg does not contain a /, a path search is performed on the first arg to determine the name of the script to execute. The script arg must have execute permission, and any setuid and setgid settings will be ignored. If the script is not found on the path, arg is processed as if it named a built-in command or function. Commands are then read as described below, and the shell interprets these options when it's invoked:

-D — do not execute the script, but output the set of double quoted strings preceded by a $. These strings are needed for localization of the script to different locales. 🌈
-E — reads the file named by the ENV variable or by $HOME/.kshrc if not defined, after the profiles.
-c — if the -c option is present, then commands are read from the first arg. Any remaining arguments become positional parameters starting at 0.
-s — if the -s option is present or if no arguments remain, then commands are read from the standard input. Shell output, except for the output of the Special Commands listed above, is written to file descriptor 2.
-i — if the -i option is present or if the shell input and output are attached to a terminal (as told by tcgetattr(2)), then this shell is interactive. In this case TERM is ignored (so that kill 0 does not kill an interactive shell) and INTR is caught and ignored (so that wait is ). In all cases, QUIT is ignored by the shell.

not me reproducing that sentence exactly how the original left it — it's literally cut off in the source, so I'm not out here inventing the rest of it 💀 no cap, that's the page.

-r — if the -r option is present, the shell is a restricted shell.
-D — a list of all double quoted strings that are preceded by a $ will be printed on standard output and the shell will exit. This set of strings will be subject to language translation when the locale is not C or POSIX. No commands will be executed. (yes, -D shows up twice in the page, I'm just relaying the message 🫶)
-P — if -P or -o profile is present, the shell is a profile shell (see pfexec(1)).
-R filename — the -R filename option is used to generate a cross reference database that can be used by a separate utility to find definitions and references for variables and commands.

The remaining options and arguments are described under the set command above. An optional - as the first argument is ignored.

🔒 Rksh Only. (restricted shell hours)

Rksh is used to set up login names and execution environments whose capabilities are more controlled than those of the standard shell. The actions of rksh are identical to those of ksh, except that these things are disallowed:

Unsetting the restricted option.
changing directory (see cd(1)),
setting or unsetting the value or attributes of SHELL, ENV, FPATH, or PATH,
specifying path or command names containing /,
redirecting output (>, >|, <>, and >>).
adding or deleting built-in commands.
using command -p to invoke a command.

The restrictions above are enforced after .profile and the ENV files are interpreted. So the setup gets to happen, then the walls come up 💅

When a command to be executed is found to be a shell procedure, rksh invokes ksh to execute it. Thus, it's possible to provide to the end-user shell procedures that have access to the full power of the standard shell, while imposing a limited menu of commands — and this scheme assumes that the end-user does not have write and execute permissions in the same directory. important assumption, don't skip it 🎀

The net effect of these rules is that the writer of the .profile has complete control over user actions, by performing guaranteed setup actions and leaving the user in an appropriate directory (probably not the login directory).

The system administrator often sets up a directory of commands (e.g., /usr/rbin) that can be safely invoked by rksh.

💥 EXIT STATUS (how it goes out)

Errors detected by the shell — like syntax errors — cause the shell to return a non-zero exit status. If the shell is being used non-interactively, then execution of the shell file is abandoned, unless the error occurs inside a subshell, in which case the subshell is abandoned instead. Otherwise, the shell returns the exit status of the last command executed (see also the exit command above).

Run time errors detected by the shell are reported by printing the command or function name and the error condition. If the line number that the error occurred on is greater than one, then the line number is also printed in square brackets ([]) after the command or function name. so you get the receipts with line numbers, iconic 🔥

📁 FILES (the whole map)

/etc/profile — the system wide initialization file, executed for login shells.
$HOME/.profile — the personal initialization file, executed for login shells after /etc/profile.
$HOME/..kshrc — default personal initialization file, executed for interactive shells when ENV is not set.
/etc/suid_profile — alternative initialization file, executed instead of the personal initialization file when the real and effective user or group id do not match. sus? no, just security bestie 🧚
/dev/null — NULL device.

👀 SEE ALSO (the whole friend group)

cat(1), cd(1), chmod(1), cut(1), egrep(1), echo(1), emacs(1), env(1), fgrep(1), gmacs(1), grep(1), newgrp(1), pfexec(1), stty(1), test(1), umask(1), vi(1), dup(2), exec(2), fork(2), getpwnam(3), ioctl(2), lseek(2), paste(1), pathconf(2), pipe(2), sysconf(2), umask(2), ulimit(2), wait(2), wctrans(3), rand(3), a.out(5), profile(5), environ(7).

Morris I. Bolsky and David G. Korn, The New KornShell Command and Programming Language, Prentice Hall, 1995.

POSIX - Part 2: Shell and Utilities, IEEE Std 1003.2-1992, ISO/IEC 9945-2, IEEE, 1993.

💀 CAVEATS 💀

okay bestie, this is the "learn from my chaos" section — the little gremlins and gotchas that live in ksh. read these, fr fr, they will save you a whole afternoon of screaming at your terminal 😭

so picture this: you run a command, and then somebody installs a command with the same name in a directory that sits earlier in your search path than the directory where the original command was found. plot twist — the shell will just keep on exec'ing the original command. no cap. the fix? use the -t option of the alias command to correct this situation. slay 💅
some very old shell scripts contain a ^ as a synonym for the pipe character |. yes really. ancient lore. 🧚
if you use the hist built-in command inside a compound command, the whole command will literally disappear from the history file. not me losing my own receipts 🙈
the built-in command . file reads the whole file before any commands are executed. so like… any alias and unalias commands in that file will not apply to any commands defined in that file. it's giving "read the whole group chat before replying" energy 💀
traps are not processed while a job is waiting for a foreground process. so a trap on CHLD won't be executed until the foreground job terminates. patience, queen 👑
and my personal fave: it is a good idea to leave a space after the comma operator in arithmetic expressions, so the comma doesn't get interpreted as the decimal point character in certain locales. yes, locales will absolutely do that to you 🌍😭

tl;dr — nothing here is broken, it's just the shell being its iconic little self. know the vibes, avoid the chaos 🫶

and that's a wrap on KSH(1), bestie — the whole page, start to finish 🌈💖 this has been the KSH(1) manual page, and it ate, no crumbs, periodt. now go write some unhinged shell scripts and make me proud 👑✨🎀

📦 where this page comes from

opensuse-leap 16.0: ksh 93vu-bp160.1.33 · CPL-1.0 AND EPL-1.0
opensuse-leap 16.0: ksh 93vu-bp160.1.33 · CPL-1.0 AND EPL-1.0
opensuse-leap 16.0: ksh 93vu-bp160.1.33 · CPL-1.0 AND EPL-1.0
opensuse-leap 16.0: ksh 93vu-bp160.1.33 · CPL-1.0 AND EPL-1.0
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-04: a language model's rewrite of the original, under its terms