DASH(1)

📦
version 0.5.13.4 · 7 versions
, in alpine 3.23, alpine 3.24, arch rolling, fedora 44, nixos 26.05

💖 DASH(1) — General Commands Manual 💖

okay bestie, so DASH(1), section 1, General Commands Manual. that's the whole header, we're moving on ✨

✨ NAME ✨

dash — command interpreter (shell)

✨ SYNOPSIS ✨

dash [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
     [+o option_name] [command_file [argument ...]]
dash -c [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
     [+o option_name] command_string [command_name [argument ...]]
dash -s [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
     [+o option_name] [argument ...]

🌸 DESCRIPTION 🌸

so dash is the standard command interpreter for the system, like the default one, the moment 🫶. the current version of dash is in the process of being changed to conform with the POSIX 1003.2 and 1003.2a specifications for the shell. this version has a lot of features that make it look kinda similar to the Korn shell in some respects, but bestie, it is not a Korn shell clone (go look at ksh(1) if you want that). only features designated by POSIX, plus a few Berkeley extensions, are being incorporated into this shell. and btw — this man page is not meant to be a tutorial or a complete specification of the shell. it's giving reference material, not a study guide 💅

🦋 Overview

the shell is a command that reads lines from either a file or the terminal, interprets them, and generally executes other commands. it's literally the program that's running when a user logs into the system (although a user can pick a different shell with the chsh(1) command 👀).

the shell implements a language that has flow control constructs, a macro facility that gives you a whole variety of features on top of just data storage, plus built in history and line editing capabilities. it incorporates many features to help with interactive use, and it has the advantage that the interpretative language is common to both interactive and non-interactive use (shell scripts). like, commands can be typed directly to the running shell, or they can be put into a file and the file can be executed directly by the shell. same language, two vibes, iconic ✨

🌈 Invocation

if no args are present and if the standard input of the shell is connected to a terminal (or if the -i flag is set), and the -c option is not present, then the shell is considered an interactive shell. an interactive shell generally prompts before each command and handles programming and command errors differently (as described below).

when it first starts up, the shell inspects argument 0, and if it begins with a dash ‘-’, the shell is also considered a login shell. this is normally done automatically by the system when the user first logs in. a login shell first reads commands from the files /etc/profile and .profile if they exist.

if the environment variable ENV is set on entry to an interactive shell, or is set in the .profile of a login shell, the shell next reads commands from the file named in ENV. so basically: a user should place commands that are to be executed only at login time in the .profile file, and commands that are executed for every interactive shell inside the ENV file. to set the ENV variable to some file, place the following line in your .profile of your home directory

ENV=$HOME/.shinit; export ENV

substituting for “.shinit” any filename you wish 💫

if command line arguments besides the options have been specified, then the shell treats the first argument as the name of a file from which to read commands (a shell script), and the remaining arguments are set as the positional parameters of the shell ($1, $2, etc). otherwise, the shell reads commands from its standard input.

🎀 Argument List Processing 🎀

all of the single letter options that have a corresponding name can be used as an argument to the -o option. the set -o name is provided next to the single letter option in the description below. specifying a dash “-” turns the option on, while using a plus “+” disables the option. the following options can be set from the command line or with the set builtin (described later).

  • -a allexport — export all variables assigned to.
  • -c — read commands from the command_string operand instead of from the standard input. special parameter 0 will be set from the command_name operand and the positional parameters ($1, $2, etc.) set from the remaining argument operands.
  • -C noclobber — don't overwrite existing files with “>”.
  • -e errexit — if not interactive, exit immediately if any untested command fails. the exit status of a command is considered to be explicitly tested if the command is used to control an if, elif, while, or until; or if the command is the left hand operand of an “&&” or “||” operator.
  • -f noglob — disable pathname expansion.
  • -n noexec — if not interactive, read commands but do not execute them. this is useful for checking the syntax of shell scripts.
  • -u nounset — write a message to standard error when attempting to expand a variable that is not set, and if the shell is not interactive, exit immediately.
  • -v verbose — the shell writes its input to standard error as it is read. useful for debugging.
  • -x xtrace — write each command to standard error (preceded by a ‘+ ’) before it is executed. useful for debugging.
  • -I ignoreeof — ignore EOF's from input when interactive.
  • -i interactive — force the shell to behave interactively.
  • -l — make dash act as if it had been invoked as a login shell.
  • -m monitor — turn on job control (set automatically when interactive).
  • -s stdin — read commands from standard input (set automatically if no file arguments are present). this option has no effect when set after the shell has already started running (i.e. with set). 🙈
  • -V vi — enable the built-in vi(1) command line editor (disables -E if it has been set).
  • -E emacs — enable the built-in emacs(1) command line editor (disables -V if it has been set).
  • -b notify — enable asynchronous notification of background job completion. (UNIMPLEMENTED for 4.4alpha 💀)

🧚 Lexical Structure

the shell reads input in terms of lines from a file and breaks it up into words at whitespace (blanks and tabs), and at certain sequences of characters that are special to the shell called “operators”. there are two types of operators: control operators and redirection operators (their meaning is discussed later). following is a list of operators:

  • Control operators:
& && ( ) ; ;; | || <newline>
  • Redirection operators:
< > >| << >> <& >& <<- <>

💜 Quoting

quoting is used to remove the special meaning of certain characters or words to the shell, like operators, whitespace, or keywords. there are three types of quoting: matched single quotes, matched double quotes, and backslash.

🌸 Backslash

a backslash preserves the literal meaning of the following character, with the exception of ⟨newline⟩. a backslash preceding a ⟨newline⟩ is treated as a line continuation.

🌸 Single Quotes

enclosing characters in single quotes preserves the literal meaning of all the characters (except single quotes, making it impossible to put single-quotes in a single-quoted string). yeah. that's just how it is bestie 😭

🌸 Double Quotes

enclosing characters within double quotes preserves the literal meaning of all characters except dollarsign ($), backquote (`), and backslash (\). the backslash inside double quotes is historically weird, and serves to quote only the following characters:

$ ` " \ <newline>.

otherwise it remains literal.

👑 Reserved Words

reserved words are words that have special meaning to the shell and are recognized at the beginning of a line and after a control operator. the following are reserved words:

!       elif    fi      while   case
else    for     then    {       }
do      done    until   if      esac

their meaning is discussed later.

⭐ Aliases

an alias is a name and corresponding value set using the alias(1) builtin command. whenever a reserved word may occur (see above), and after checking for reserved words, the shell checks the word to see if it matches an alias. if it does, it replaces it in the input stream with its value. for example, if there is an alias called “lf” with the value “ls -F”, then the input:

lf foobar ⟨return⟩

would become

ls -F foobar ⟨return⟩

aliases provide a convenient way for naive users to create shorthands for commands without having to learn how to create functions with arguments. they can also be used to create lexically obscure code. this use is discouraged. 🫣

💫 Commands

the shell interprets the words it reads according to a language, the specification of which is outside the scope of this man page (refer to the BNF in the POSIX 1003.2 document). essentially though, a line is read and if the first word of the line (or after a control operator) is not a reserved word, then the shell has recognized a simple command. otherwise, a complex command or some other special construct may have been recognized.

🍓 Simple Commands

if a simple command has been recognized, the shell performs the following actions:

  1. leading words of the form “name=value” are stripped off and assigned to the environment of the simple command. redirection operators and their arguments (as described below) are stripped off and saved for processing.
  2. the remaining words are expanded as described in the section called “Expansions”, and the first remaining word is considered the command name and the command is located. the remaining words are considered the arguments of the command. if no command name resulted, then the “name=value” variable assignments recognized in item 1 affect the current shell.
  3. redirections are performed as described in the next section.

🦋 Redirections

redirections are used to change where a command reads its input or sends its output. in general, redirections open, close, or duplicate an existing reference to a file. the overall format used for redirection is:

[n] redir-op file

more coming, bestie — don't go anywhere 💖

where redir-op is one of those redirection operators we already met, bestie. Here's the whole menu of possible redirections. The [n] is an optional number from 0 to 9, written like 3 (NOT like [3], okay? the brackets are a lie), and it points at a file descriptor. 💅

  • [n]> file — sends standard output (or fd n) off to file.
  • [n]>| file — same thing, but it overrides the -C option. (yes, that | is doing something, it's not just vibes)
  • [n]>> file — appends standard output (or fd n) to file instead of clobbering it.
  • [n]< file — pulls standard input (or fd n) in from file.
  • [n1]<&n2 — copies file descriptor n2 and makes it stdin (or fd n1).
  • [n]<&- — closes standard input (or fd n). bye bestie 👋
  • [n1]>&n2 — copies file descriptor n2 and makes it stdout (or fd n1).
  • [n]>&- — closes standard output (or fd n).
  • [n]<> file — opens file for reading AND writing on standard input (or fd n). it's giving versatile ✨

The next one is the one everyone calls a "here-document" 🎀

[n]<< delimiter
      here-doc-text ...
delimiter

Every line of text after that, all the way down until the delimiter shows up again, gets saved away and handed to the command on standard input — or on file descriptor n if you specified one. Here's the tea though: if the delimiter on that first line is quoted, then the here-doc-text is treated completely literally. If it's not quoted, the text gets put through parameter expansion, command substitution, and arithmetic expansion (all that stuff from the "Expansions" section). And if the operator is <<- instead of <<, then leading tabs in the here-doc-text get stripped. 🌸

✨ Search and Execution ✨

Okay so there are three types of commands, and the shell searches for yours (by name) in this exact order: shell functions, builtin commands, and normal programs. Each one gets executed a totally different way, and honestly? iconic behavior. 👑

When a shell function runs, all the shell positional parameters get set to the arguments of the function — except $0, which stays exactly the same, she's not changing for anybody. The variables you explicitly drop into the command's environment (by writing assignments before the function name) become local to the function and get set to the values you gave. Then the command inside the function definition executes. When it's done, the positional parameters get restored to their original values. And all of this happens inside the current shell. no fork, no drama. 💖

Shell builtins are executed internally to the shell, without spawning a new process. lowkey efficient.

Otherwise — if the command name doesn't match a function or a builtin — the shell goes hunting for it as a normal program out in the file system (more on that in the next section). When a normal program gets executed, the shell runs the program and passes the arguments and the environment along to it. But here's the plot twist 😭: if the program is NOT a normal executable file (like, it doesn't start with the "magic number" whose ASCII representation is "#!", so execve(2) returns ENOEXEC), then the shell will interpret the program in a subshell. In that case the child shell reinitializes itself, so the effect is like a brand new shell got invoked to handle the ad-hoc shell script — except the location of hashed commands from the parent shell will still be remembered by the child. bestie remembers where she came from 🫶

Heads up: previous versions of this document and the source code itself misleadingly and sporadically refer to a shell script without a magic number as a "shell procedure". that name is a jumpscare, ignore it.

When it's locating a command, the shell first checks whether it has a shell function with that name. Then it looks for a builtin command with that name. If no builtin is found, one of two things happens:

  1. Command names containing a slash are simply executed without performing any searches. no search party needed, she's right there. 💅
  2. The shell searches each entry in PATH in turn for the command. The value of the PATH variable should be a series of entries separated by colons. Each entry is a directory name. The current directory may be indicated implicitly by an empty directory name, or explicitly by a single period. ⭐

💜 Command Exit Status 💜

Every command has an exit status, and that exit status can influence how other shell commands behave. The paradigm is simple: a command exits with zero for normal or success, and non-zero for failure, error, or a false indication. The man page for each command should tell you the various exit codes and what they mean. Builtin commands return exit codes too, and so does an executed shell function. everybody's got receipts. 🧾

If a command consists entirely of variable assignments, then the exit status of the command is the exit status of the last command substitution, if there is one — otherwise it's 0.

🦋 Complex Commands 🦋

Complex commands are combinations of simple commands with control operators or reserved words, together creating a bigger complex command. More generally, a command is one of these:

  • simple command
  • pipeline
  • list or compound-list
  • compound command
  • function definition

Unless otherwise stated, the exit status of a command is the exit status of the last simple command executed by that command. periodt. 💅

🔥 Pipelines 🔥

A pipeline is a sequence of one or more commands separated by the control operator |. The standard output of every command except the last one gets connected to the standard input of the next command. The standard output of the last command is inherited from the shell, as usual.

The format for a pipeline is:

[!] command1 [| command2 ...]

The standard output of command1 is connected to the standard input of command2. And listen — the standard input, standard output, or both of a command is considered to be assigned by the pipeline before any redirection specified by redirection operators that are part of the command. order matters, always. ✨

If the pipeline is not in the background (we'll get to that later), the shell waits for all commands to complete. patient queen.

Now, the pipefail tea ☕: if the pipefail option was enabled when the shell began execution of the pipeline, the pipeline's exit status is the exit status of the last command specified in the pipeline that exited with non-zero status, or zero if all commands in the pipeline exited with a status of zero. If the pipefail option was not enabled, the pipeline's exit status is just the exit status of the last command specified in the pipeline — the exit statuses of any other commands are not used, sorry to them. And if the reserved word ! precedes the pipeline, its exit status is the logical NOT of the exit status described above. 🙈

Because the pipeline assigns standard input or standard output or both before redirection happens, redirection can modify it. For example:

$ command1 2>&1 | command2

That sends both the standard output and standard error of command1 to the standard input of command2. slay, that's the good stuff. 💖

A ; or ⟨newline⟩ terminator causes the preceding AND-OR-list (described next) to be executed sequentially; a & causes asynchronous execution of the preceding AND-OR-list.

Real talk: unlike some other shells, each process in the pipeline is a child of the invoking shell — unless it's a shell builtin, in which case it executes in the current shell, but any effect it has on the environment gets wiped. 😭

🌸 Background Commands – & 🌸

If a command is terminated by the control operator ampersand (&), the shell executes the command asynchronously — meaning the shell does not wait for the command to finish before executing the next command. she's got places to be, bestie. 🏃‍♀️💨

The format for running a command in background is:

command1 & [command2 & ...]

If the shell is not interactive, the standard input of an asynchronous command is set to /dev/null. it's giving silence, it's giving nothing. 💀

🎀 Lists – Generally Speaking 🎀

A list is a sequence of zero or more commands separated by newlines, semicolons, or ampersands, and optionally terminated by one of these three characters. The commands in a list are executed in the order they're written. If a command is followed by an ampersand, the shell starts the command and immediately proceeds onto the next command; otherwise it waits for the command to terminate before proceeding to the next one. patience is a virtue or whatever ✨

💅 Short-Circuit List Operators 💅

&& and || are AND-OR list operators. && executes the first command, and then executes the second command if and only if the exit status of the first command is zero. || is similar, but it executes the second command if and only if the exit status of the first command is nonzero. And && and || both have the same priority. they're equals, no competition. 👑

👑 Flow-Control Constructs – if, while, for, case 👑

The syntax of the if command is:

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

The syntax of the while command is:

while list
do   list
done

Those two lists get executed repeatedly while the exit status of the first list is zero. The until command is similar, but it has the word until in place of while, which makes it repeat until the exit status of the first list is zero. same energy, opposite direction. 🔄

The syntax of the for command is:

for variable [ in [ word ... ] ]
do   list
done

The words following in get expanded, and then the list is executed repeatedly with the variable set to each word in turn. Omitting in word ... is equivalent to writing in "$@". 🦋

The syntax of the break and continue commands is:

break [ num ]
continue [ num ]

break terminates the num innermost for or while loops. continue continues with the next iteration of the innermost loop. And guess what — these are implemented as builtin commands. builtin and iconic, obviously. 💖

The syntax of the case command is:

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

The pattern can actually be one or more patterns (see "Shell Patterns", described later), separated by | characters. And the ( character before the pattern is optional — she's just there if you want her. ✨

🫶 Grouping Commands Together 🫶

Commands may be grouped by writing either:

(list)

or:

{ list; }

The first one executes the commands in a subshell. Builtin commands grouped into a (list) will not affect the current shell. The second form does not fork another shell, so it's slightly more efficient. Grouping commands together like this lets you redirect their output as though they were one single program:

{ printf " hello " ; printf " world\n" ; } > greeting
Note that } must follow a control operator (here, ;) so it gets recognized as a reserved word and not as another command argument. do not forget the semicolon, I am begging you 😭

⭐ Functions ⭐

The syntax of a function definition is:

name () command

A function definition is an executable statement; when it's executed it installs a function named name and returns an exit status of zero. The command is normally a list enclosed between { and }.

Variables may be declared to be local to a function by using a local command. This should appear as the first statement of a function, and the syntax is:

local [variable | -] ...

okay so local? it's a builtin command. 💅 Not some external binary you gotta go find, it lives inside the shell. Bestie behavior fr.

When you make a variable local, it inherits the initial value and the exported and readonly flags from the variable with the same name in the surrounding scope, if there is one. No surrounding twin? Then the variable is just… initially unset. Iconic, but empty. 🫥

And here's the part that trips everyone up: the shell uses dynamic scoping. So if you make the variable x local to function f, and then f calls function g, then references to the variable x made inside g will refer to the variable x declared inside f — NOT to the global variable named x. It's giving "what happens in f, stays in `f"'s call stack. 😭

The only special parameter that can be made local is “-”. Making “-” local means any shell options that are changed via the set command inside the function get restored to their original values when the function returns. Chef's kiss. 🤌

The syntax of the return command is:

return [exitstatus]

It terminates the currently executing function. And yes, return is implemented as a builtin command too. 🎀

✨ Variables and Parameters ✨

The shell maintains a set of parameters. A parameter denoted by a name is called a variable. When starting up, the shell turns all the environment variables into shell variables. New variables can be set using the form:

name=value

Variables set by the user must have a name consisting solely of alphabetics, numerics, and underscores — and the first of those must not be numeric. (So 2cool is a no. cool2 is a yes. slay.) A parameter can also be denoted by a number or a special character, as explained below. 👇

✨ Positional Parameters ✨

A positional parameter is a parameter denoted by a number (n > 0). The shell sets these initially to the values of its command line arguments that follow the name of the shell script. The set builtin can also be used to set or reset them. Very demure, very mindful. 🎀

✨ Special Parameters ✨

A special parameter is a parameter denoted by one of the following special characters. The value of the parameter is listed right next to its character, so you literally cannot miss it. 💖

  • * — Expands to the positional parameters, starting from one. When the expansion occurs within a double-quoted string it expands to a single field with the value of each parameter separated by the first character of the IFS variable, or by a ⟨space⟩ if IFS is unset.
  • @ — Expands to the positional parameters, starting from one. When the expansion occurs within double-quotes, each positional parameter expands as a separate argument. If there are no positional parameters, the expansion of @ generates zero arguments, even when @ is double-quoted. What this basically means, for example, is if $1 is “abc” and $2 is “def ghi”, then "$@" expands to the two arguments:
"abc" "def ghi"
  • # — Expands to the number of positional parameters. 📊
  • ? — Expands to the exit status of the most recent pipeline. 👀
  • - (Hyphen.) — Expands to the current option flags (the single-letter option names concatenated into a string) as specified on invocation, by the set builtin command, or implicitly by the shell. 🚩
  • $ — Expands to the process ID of the invoked shell. A subshell retains the same value of $ as its parent. (Family resemblance, literally. 💅)
  • ! — Expands to the process ID of the most recent background command executed from the current shell. For a pipeline, the process ID is that of the last command in the pipeline. 🏃‍♀️
  • 0 (Zero.) — Expands to the name of the shell or shell script. 🌟

✨ Word Expansions ✨

This clause describes the various expansions that are performed on words. Not all expansions are performed on every word, as explained later. So don't come for me. 🙈

Tilde expansions, parameter expansions, command substitutions, arithmetic expansions, and quote removals that occur within a single word expand to a single field. It is only field splitting or pathname expansion that can create multiple fields from a single word. The single exception to this rule is the expansion of the special parameter @ within double-quotes, as was described above. 👑

The order of word expansion is:

  1. Tilde Expansion, Parameter Expansion, Command Substitution, Arithmetic Expansion (these all occur at the same time).
  2. Field Splitting is performed on fields generated by step (1) unless the IFS variable is null.
  3. Pathname Expansion (unless set -f is in effect).
  4. Quote Removal.

The $ character is used to introduce parameter expansion, command substitution, or arithmetic evaluation. 💲

✨ Tilde Expansion (substituting a user's home directory) ✨

A word beginning with an unquoted tilde character (~) is subjected to tilde expansion. All the characters up to a slash (/) or the end of the word are treated as a username and are replaced with the user's home directory. 🏠

If the username is missing (as in ~/foobar), the tilde is replaced with the value of the HOME variable (the current user's home directory). No username, no problem. 🫶

✨ Parameter Expansion ✨

The format for parameter expansion is as follows:

${expression}

where expression consists of all characters until the matching “}”. Any “}” escaped by a backslash or within a quoted string, and characters in embedded arithmetic expansions, command substitutions, and variable expansions, are not examined in determining the matching “}”. Sneaky little braces. 😤

The simplest form for parameter expansion is:

${parameter}

The value, if any, of parameter is substituted.

The parameter name or symbol can be enclosed in braces, which are optional except for positional parameters with more than one digit or when parameter is followed by a character that could be interpreted as part of the name.

If a parameter expansion occurs inside double-quotes:

  1. Pathname expansion is not performed on the results of the expansion.
  2. Field splitting is not performed on the results of the expansion, with the exception of @.

In addition, a parameter expansion can be modified by using one of the following formats. 💅

  • ${parameter:-word} — Use Default Values. If parameter is unset or null, the expansion of word is substituted; otherwise, the value of parameter is substituted.
  • ${parameter:=word} — Assign Default Values. If parameter is unset or null, the expansion of word is assigned to parameter. In all cases, the final value of parameter is substituted. Only variables, not positional parameters or special parameters, can be assigned in this way. ⚠️
  • ${parameter:?[word]} — Indicate Error if Null or Unset. If parameter is unset or null, the expansion of word (or a message indicating it is unset if word is omitted) is written to standard error and the shell exits with a nonzero exit status. Otherwise, the value of parameter is substituted. An interactive shell need not exit. 😱
  • ${parameter:+word} — Use Alternative Value. If parameter is unset or null, null is substituted; otherwise, the expansion of word is substituted.

In the parameter expansions shown previously, use of the colon in the format results in a test for a parameter that is unset or null; omission of the colon results in a test for a parameter that is only unset. Small colon, big difference, no cap. 🎀

  • ${#parameter} — String Length. The length in characters of the value of parameter. 📏

The following four varieties of parameter expansion provide for substring processing. In each case, pattern matching notation (see “Shell Patterns”), rather than regular expression notation, is used to evaluate the patterns. If parameter is * or @, the result of the expansion is unspecified. Enclosing the full parameter expansion string in double-quotes does not cause the following four varieties of pattern characters to be quoted, whereas quoting characters within the braces has this effect. 🧠

  • ${parameter%word} — Remove Smallest Suffix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the smallest portion of the suffix matched by the pattern deleted.
  • ${parameter%%word} — Remove Largest Suffix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the largest portion of the suffix matched by the pattern deleted.
  • ${parameter#word} — Remove Smallest Prefix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the smallest portion of the prefix matched by the pattern deleted.
  • ${parameter##word} — Remove Largest Prefix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the largest portion of the prefix matched by the pattern deleted.

✨ Command Substitution ✨

Command substitution allows the output of a command to be substituted in place of the command name itself. 🎯

Command substitution occurs when the command is enclosed as follows:

$(command)

or (the “backquoted” version):

`command`

The shell expands the command substitution by executing command in a subshell environment and replacing the command substitution with the standard output of the command, removing sequences of one or more ⟨newline⟩s at the end of the substitution. (Embedded ⟨newline⟩s before the end of the output are not removed; however, during field splitting, they may be translated into ⟨space⟩s, depending on the value of IFS and quoting that is in effect.) 😮‍💨

✨ Arithmetic Expansion ✨

Arithmetic expansion provides a mechanism for evaluating an arithmetic expression and substituting its value. Math class but make it useful. 🔢

The format for arithmetic expansion is as follows:

$((expression))

The expression is treated as if it were in double-quotes, except that a double-quote inside the expression is not treated specially. The shell expands all tokens in the expression for parameter expansion, command substitution, and quote removal.

Next, the shell treats this as an arithmetic expression and substitutes the value of the expression. 🧮✨

🫧 White Space Splitting (Field Splitting) 🫧

okay so bestie, after parameter expansion, command substitution, and arithmetic expansion, the shell scans the results of expansions and substitutions that did not occur in double-quotes for field splitting, and multiple fields can result. periodt.

The shell treats each character of IFS as a delimiter and uses those delimiters to split the results of parameter expansion and command substitution into fields.

If IFS is empty, field splitting yields no fields if the input string was empty, and one string with the unchanged value of the input otherwise. For example, with the default IFS, read -r l will remove any initial whitespace, but IFS= read -r l will leave the entire line in l. iykyk 💅

🌈 Pathname Expansion (File Name Generation) 🌈

Unless the -f flag is set, file name generation is performed after word splitting is complete. Each word is viewed as a series of patterns, separated by slashes. The process of expansion replaces the word with the names of all existing files whose names can be formed by replacing each pattern with a string that matches the specified pattern. There are two restrictions on this: first, a pattern cannot match a string containing a slash, and second, a pattern cannot match a string starting with a period unless the first character of the pattern is a period. The next section describes the patterns used for both Pathname Expansion and the case command. no cap ✨

🧚 Shell Patterns 🧚

A pattern consists of normal characters, which match themselves, and meta-characters. The meta-characters are !, *, ?, and [. These characters lose their special meanings if they are quoted. When command or variable substitution is performed and the dollar sign or back quotes are not double quoted, the value of the variable or the output of the command is scanned for these characters and they are turned into meta-characters.

An asterisk (*) matches any string of characters. A question mark (?) matches any single character. A left bracket ([) introduces a character class. The end of the character class is indicated by a (]); if the ] is missing then the [ matches a [ rather than introducing a character class. A character class matches any of the characters between the square brackets. A range of characters may be specified using a minus sign. The character class may be complemented by making an exclamation point the first character of the character class.

To include a ] in a character class, make it the first character listed (after the !, if any). To include a minus sign, make it the first or last character listed. slay 💖

👑 Builtins 👑

This section lists the builtin commands which are builtin because they need to perform some operation that can't be performed by a separate process. In addition to these, there are several other commands that may be builtin for efficiency (e.g. printf(1), echo(1), test(1), etc).

  • :
  • true — A null command that returns a 0 (true) exit value.
  • false — A null command that returns a 1 (false) exit value.
  • . file — The commands in the specified file are read and executed by the shell.
  • alias [name[=string ...]] — If name=string is specified, the shell defines the alias name with value string. If just name is specified, the value of the alias name is printed. With no arguments, the alias builtin prints the names and values of all defined aliases (see unalias).
  • bg [job] ... — Continue the specified jobs (or the current job if no jobs are given) in the background.
  • command [-p] [-v] [-V] command [arg ...] — Execute the specified command but ignore shell functions when searching for it. (This is useful when you have a shell function with the same name as a builtin command.)
    • -p — search for command using a PATH that guarantees to find all the standard utilities.
    • -V — Do not execute the command but search for the command and print the resolution of the command search. This is the same as the type builtin.
    • -v — Do not execute the command but search for the command and print the absolute pathname of utilities, the name for builtins or the expansion of aliases.
  • cd|chdir -, cd|chdir [-LP] [directory] — Switch to the specified directory (default HOME). If an entry for CDPATH appears in the environment of the cd command or the shell variable CDPATH is set and the directory name does not begin with a slash, then the directories listed in CDPATH will be searched for the specified directory. The format of CDPATH is the same as that of PATH. If a single dash is specified as the argument, it will be replaced by the value of OLDPWD. The cd command will print out the name of the directory that it actually switched to if this is different from the name that the user gave. These may be different either because the CDPATH mechanism was used or because the argument is a single dash. The -P option causes the physical directory structure to be used, that is, all symbolic links are resolved to their respective values. The -L option turns off the effect of any preceding -P options.
  • echo [-n] args... — Print the arguments on the standard output, separated by spaces. Unless the -n option is present, a newline is output following the arguments.
    • If any of the following sequences of characters is encountered during output, the sequence is not output. Instead, the specified action is performed:
      • \b — A backspace character is output.
      • \c — Subsequent output is suppressed. This is normally used at the end of the last argument to suppress the trailing newline that echo would otherwise output.
      • \f — Output a form feed.
      • \n — Output a newline character.
      • \r — Output a carriage return.
      • \t — Output a (horizontal) tab character.
      • \v — Output a vertical tab.
      • \0digits — Output the character whose value is given by zero to three octal digits. If there are zero digits, a nul character is output.
      • \\ — Output a backslash.
    • All other backslash sequences elicit undefined behaviour.
  • eval string ... — Concatenate all the arguments with spaces. Then re-parse and execute the command.
  • exec [command arg ...] — Unless command is omitted, the shell process is replaced with the specified program (which must be a real program, not a shell builtin or function). Any redirections on the exec command are marked as permanent, so that they are not undone when the exec command finishes.
  • exit [exitstatus] — Terminate the shell process. If exitstatus is given it is used as the exit status of the shell; otherwise the exit status of the preceding command is used.
  • export name ..., export -p — The specified names are exported so that they will appear in the environment of subsequent commands. The only way to un-export a variable is to unset it. The shell allows the value of a variable to be set at the same time it is exported by writing
export name=value

With no arguments the export command lists the names of all exported variables. With the -p option specified the output will be formatted suitably for non-interactive use.

  • fc [-e editor] [first [last]]
  • fc -l [-nr] [first [last]]
  • fc -s [old=new] [first] — The fc builtin lists, or edits and re-executes, commands previously entered to an interactive shell.
    • -e editor — Use the editor named by editor to edit the commands. The editor string is a command name, subject to search via the PATH variable. The value in the FCEDIT variable is used as a default when -e is not specified. If FCEDIT is null or unset, the value of the EDITOR variable is used. If EDITOR is null or unset, ed(1) is used as the editor.
    • -l (ell) — List the commands rather than invoking an editor on them. The commands are written in the sequence indicated by the first and last operands, as affected by -r, with each command preceded by the command number.
    • -n — Suppress command numbers when listing with -l.
    • -r — Reverse the order of the commands listed (with -l) or edited (with neither -l nor -s).
    • -s — Re-execute the command without invoking an editor.
    • first, last — Select the commands to list or edit. The number of previous commands that can be accessed are determined by the value of the HISTSIZE variable. The value of first or last or both are one of the following:
      • [+]number — A positive number representing a command number; command numbers can be displayed with the -l option.
      • -number — A negative decimal number representing the command that was executed number of commands previously. For example, -1 is the immediately previous command.
    • string — A string indicating the most recently entered command that begins with that string. If the old=new operand is not also specified with -s, the string form of the first operand cannot contain an embedded equal sign.
    • The following environment variables affect the execution of fc:
      • FCEDIT — Name of the editor to use.
      • HISTSIZE — The number of previous commands that are accessible.
  • fg [job] — Move the specified job or the current job to the foreground.
  • getopts optstring var [arg ...] — The POSIX getopts command, not to be confused with the Bell Labs-derived getopt(1).
    • The first argument should be a series of letters, each of which may be optionally followed by a colon to indicate that the option requires an argument. The variable specified is set to the parsed option.
    • The getopts command deprecates the older getopt(1) utility due to its handling of arguments containing whitespace.

The getopts builtin is literally how you snatch options and their arguments out of a list of parameters, bestie. When you invoke it, getopts drops the value of the next option from the option string in the list into the shell variable you named with var, and tucks its index into the shell variable OPTIND. When the shell gets invoked, OPTIND is initialized to 1. For every option that needs an argument, the getopts builtin slides it into the shell variable OPTARG. And if an option isn't allowed for in optstring, then OPTARG gets unset. gone. 💀

By default, the variables $1, ..., $n get inspected; but if args are specified, those get parsed instead. iykyk.

optstring is a string of recognized option letters (go look at getopt(3)). If a letter is followed by a colon, that option is expected to have an argument, which may or may not be separated from it by white space. If an option character isn't found where expected, getopts sets var to a “?”; then getopts unsets OPTARG and writes output to standard error. And if you specify a colon as the first character of optstring, all errors get ignored. periodt. ✨

After the last option, getopts returns a non-zero value and sets var to “?”.

This code fragment shows how one might process the arguments for a command that can take the options [a] and [b], and the option [c], which requires an argument:

while getopts abc: f
do
        case $f in
        a | b)  flag=$f;;
        c)      carg=$OPTARG;;
        \?)     echo $USAGE; exit 1;;
        esac
done
shift $((OPTIND - 1))

This code will accept any of the following as equivalent:

cmd -acarg file file
cmd -a -c arg file file
cmd -carg -a file file
cmd -a -carg -- file file

hash 💖

hash [command ...]

hash -r

The shell keeps a hash table that remembers the locations of commands. With no arguments whatsoever, the hash command prints out the contents of this table. Entries that haven't been looked at since the last cd command get marked with an asterisk; and ngl, it's possible for those entries to be invalid. 🙈

With arguments, the hash command removes the specified commands from the hash table (unless they're functions) and then locates them. The -r option makes the hash command delete all the entries in the hash table except for functions. bye to the whole table, except functions, they stay. 👑

jobs 🌸

jobs [-lp] [job ...]

Display the status of all the jobs, or just the specified ones:

  • By default, display the job number, currency (+-) status, if any, the job state, and its shell command.
  • -l — also output the PID of the group leader, and just the PID and shell commands of other members of the job.
  • -p — Display only leader PIDs, one per line.

kill 💅

kill [-s sigspec | -signum | -sigspec] [pid | job ...]

Equivalent to kill(1), but a job spec may also be specified. Signals can be either case-insensitive names without SIG prefixes or decimal numbers; the default is TERM. so if you don't say anything, it's TERM, that's the vibe.

kill -l [signum | exitstatus]

List available signal names without the SIG prefix (sigspecs). If signum is specified, display just the sigspec for that signal. If exitstatus is specified (that's > 128), display just the sigspec that caused it.

pwd 🦋

pwd [-LP]

The builtin command remembers what the current directory is rather than recomputing it each time. This makes it faster. However, if the current directory is renamed, the builtin version of pwd will continue to print the old name for the directory. 😭 The -P option causes the physical value of the current working directory to be shown, that is, all symbolic links are resolved to their respective values. The -L option turns off the effect of any preceding -P options.

read 🎀

read [-p prompt] [-r] variable [...]

The prompt is printed if the -p option is specified and the standard input is a terminal. Then a line is read from the standard input. The trailing newline is deleted from the line, and the line is split as described in the section on word splitting above, and the pieces are assigned to the variables in order. At least one variable must be specified. If there are more pieces than variables, the remaining pieces (along with the characters in IFS that separated them) get assigned to the last variable. If there are more variables than pieces, the remaining variables get assigned the null string. The read builtin will indicate success unless EOF is encountered on input, in which case failure is returned.

By default, unless the -r option is specified, the backslash “\” acts as an escape character, causing the following character to be treated literally. If a backslash is followed by a newline, the backslash and the newline will be deleted. 🧚

readonly ⭐

readonly name ...

readonly -p

The specified names are marked as read only, so that they cannot be subsequently modified or unset. The shell allows the value of a variable to be set at the same time it is marked read only by writing

readonly name=value

With no arguments, the readonly command lists the names of all read only variables. With the -p option specified, the output will be formatted suitably for non-interactive use.

printf ✨

printf format [value]...

printf formats and prints its arguments according to format, a character string which contains three types of objects: plain characters, which are simply copied to standard output, character escape sequences which are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive value.

Each value is treated as a string if the corresponding format specification is either b, c, or s; otherwise it is evaluated as a C constant, with the following additions:

  • A leading plus or minus sign is allowed.
  • If the leading character is a single or double quote, the value of the next byte.

The format string is reused as often as necessary until all values are consumed. Any extra format specifications are evaluated with zero or the null string.

Character escape sequences are in backslash notation as defined in ANSI X3.159-1989 (“ANSI C89”). The characters and their meanings are as follows:

  • \a — Write a <bell> character.
  • \b — Write a <backspace> character.
  • \f — Write a <form-feed> character.
  • \n — Write a <new-line> character.
  • \r — Write a <carriage return> character.
  • \t — Write a <tab> character.
  • \v — Write a <vertical tab> character.
  • \\ — Write a backslash character.
  • \num — Write an 8-bit character whose ASCII value is the 1-, 2-, or 3-digit octal number num.

Each format specification is introduced by the percent character (%). The remainder of the format specification includes, in the following order:

Zero or more of the following flags:

  • # — A #' character specifying that the value should be printed in an ``alternative form''. For b, c, d, and sformats, this option has no effect. For theoformat the precision of the number is increased to force the first character of the output string to a zero. For thex (X) format, a non-zero result has the string 0x (0X) prepended to it. For e, E, f, g, and Gformats, the result will always contain a decimal point, even if no digits follow the point (normally, a decimal point only appears in the results of those formats if a digit follows the decimal point). ForgandG` formats, trailing zeros are not removed from the result as they would otherwise be.
  • - — A minus sign `-' which specifies left adjustment of the output in the indicated field;
  • + — A `+' character specifying that there should always be a sign placed before the number when using signed formats.
  • ‘ ’ — A space specifying that a blank should be left before a positive number for a signed format. A `+' overrides a space if both are used;
  • 0 — A zero 0' character indicating that zero-padding should be used rather than blank-padding. A -' overrides a `0' if both are used;

Field Width:

An optional digit string specifying a field width; if the output string has fewer characters than the field width it will be blank-padded on the left (or right, if the left-adjustment indicator has been given) to make up the field width (note that a leading zero is a flag, but an embedded zero is part of a field width);

Precision:

An optional period, ‘.’, followed by an optional digit string giving a precision which specifies the number of digits to appear after the decimal point, for e and f formats, or the maximum number of bytes to be printed from a string (b and s formats); if the digit string is missing, the precision is treated as zero;

Format:

A character which indicates the type of format to use (one of diouxXfwEgGbcs).

A field width or precision may be ‘*’ instead of a digit string. In this case an argument supplies the field width or precision.

The format characters and their meanings are:

  • diouXx — the argument gets printed as a signed decimal (d or i), unsigned octal, unsigned decimal, or unsigned hexadecimal (X or x), respectively. pick your fighter 💅
  • f — argument printed in the style [-]ddd.ddd, where the number of d's after the decimal point is exactly the precision you specified for the argument. No precision given? You get 6 digits. Precision explicitly 0? Then no digits and no decimal point at all, we said what we said.
  • eE — argument printed in the style [-]d.ddde±dd, one digit before the decimal point and the rest of the digits matching the precision you specified; precision missing means 6 digits get produced. And an upper-case E shows up when you use the E format. ✨
  • gG — argument printed in style f or in style e (E), whichever one gives you full precision in minimum space. it's giving efficient 🎀
  • b — characters from the string argument are printed with backslash-escape sequences expanded. and bestie, there are extra backslash-escape sequences on top of the usual ones:
    • \c — causes dash to ignore any remaining characters in the string operand containing it, any remaining string operands, and any additional characters in the format operand. it just… stops caring 😭
    • \0num — write an 8-bit character whose ASCII value is the 1-, 2-, or 3-digit octal number num.
  • c — the first character of the argument is printed. just the one. iconic behavior honestly.
  • s — characters from the string argument are printed until the end is reached, or until you hit the number of bytes indicated by the precision specification; if the precision is omitted, every character in the string gets printed.
  • % — prints a %. no argument used, it just does that. 🫶
In no case does a non-existent or small field width cause truncation of a field; padding takes place only if the specified field width exceeds the actual width. like, it will not cut your field short for you. periodt.

✨ set [{ -options | +options | -- }] arg ... ✨

the set command is a triple threat, it performs three different functions:

With no arguments, it lists the values of all shell variables.

If options are given, it sets the specified option flags, or clears them as described in the section called “Argument List Processing”. Special case alert 🚨 — if the option is -o or +o and no argument is supplied, the shell prints the settings of all its options. If the option is -o, those settings print in a human-readable format; if it's +o, they print in a format suitable for reinput to the shell to affect the same option settings. so you can literally feed it back in, iykyk.

In addition to the option names listed in the “Argument List Processing” section, the following options may be specified as arguments to -o or +o:

  • pipefail — derive the exit status of a pipeline from the exit statuses of all of the commands in the pipeline, not just the last command, as described in the “Pipelines” section.

The third use of the set command is to set the values of the shell's positional parameters to the specified args. To change the positional parameters without changing any options, use -- as the first argument to set. If no args are present, the set command will clear all the positional parameters — which is equivalent to executing shift $#. 💀

🌸 shift [n] 🌸

Shift the positional parameters n times. A shift sets the value of $1 to the value of $2, the value of $2 to the value of $3, and so on, decreasing the value of $# by one. If n is greater than the number of positional parameters, shift will issue an error message, and exit with return status 2. so don't over-shift, bestie 🙈

💜 test expression 💜

💜 [ expression ] 💜

The test utility evaluates the expression and, if it evaluates to true, returns a zero (true) exit status; otherwise it returns 1 (false). If there is no expression, test also returns 1 (false).

All operators and flags are separate arguments to the test utility.

The following primaries are used to construct expression:

  • -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 (regardless of type).
  • -f file — true if file exists and is a regular file.
  • -g file — true if file exists and its set group ID flag is set.
  • -h file — true if file exists and is a symbolic link.
  • -k file — true if file exists and its sticky bit is set.
  • -n string — true if the length of string is nonzero.
  • -p file — true if file is a named pipe (FIFO).
  • -r file — true if file exists and is readable.
  • -s file — true if file exists and has a size greater than zero.
  • -t file_descriptor — true if the file whose file descriptor number is file_descriptor is open and is associated with a terminal.
  • -u file — true if file exists and its set user ID flag is set.
  • -w file — true if file exists and is writable. True indicates only that the write flag is on. The file is not writable on a read-only file system even if this test indicates true. ⚠️
  • -x file — true if file exists and is executable. True indicates only that the execute flag is on. If file is a directory, true indicates that file can be searched.
  • -z string — true if the length of string is zero.
  • -L file — true if file exists and is a symbolic link. This operator is retained for compatibility with previous versions of this program. Do not rely on its existence; use -h instead. 👑
  • -O file — true if file exists and its owner matches the effective user id of this process.
  • -G file — true if file exists and its group matches the effective group id of this process.
  • -S file — true if file exists and is a socket.
  • file1 -nt file2 — true if file1 and file2 exist and file1 is newer than file2, or if file1 exists but file2 doesn't.
  • file1 -ot file2 — true if file1 and file2 exist and file1 is older than file2, or if file2 exists but file1 doesn't.
  • file1 -ef file2 — true if file1 and file2 exist and refer to the same file.
  • string — true if string is not the null string.
  • s1 = s2 — true if the strings s1 and s2 are identical.
  • s1 != s2 — true if the strings s1 and s2 are not identical.
  • s1 < s2 — true if string s1 comes before s2 based on the ASCII value of their characters.
  • s1 > s2 — true if string s1 comes after s2 based on the ASCII value of their characters.
  • n1 -eq n2 — true if the integers n1 and n2 are algebraically equal.
  • n1 -ne n2 — true if the integers n1 and n2 are not algebraically equal.
  • n1 -gt n2 — true if the integer n1 is algebraically greater than the integer n2.
  • n1 -ge n2 — true if the integer n1 is algebraically greater than or equal to the integer n2.
  • n1 -lt n2 — true if the integer n1 is algebraically less than the integer n2.
  • n1 -le n2 — true if the integer n1 is algebraically less than or equal to the integer n2.

These primaries can be combined with the following operators:

  • ! expression — true if expression is false.
  • expression1 -a expression2 — true if both expression1 and expression2 are true.
  • expression1 -o expression2 — true if either expression1 or expression2 are true.
  • ( expression ) — true if expression is true.
heads up bestie: the -a operator has higher precedence than the -o operator. 🔥

🦋 times 🦋

Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0. cute and simple, we love that for us.

💅 trap [action signal ...] 💅

Cause the shell to parse and execute action when any of the specified signals are received. The signals are specified by signal number or as the name of the signal. If signal is 0 or EXIT, the action is executed when the shell exits normally (that is, not via an unhandled signal like SIGINT). action may be empty (''), which causes the specified signals to be ignored. With action omitted or set to -, the specified signals are set to their default action. When the shell forks off a subshell, it resets trapped (but not ignored) signals to the default action. The trap command has no effect on signals that were ignored on entry to the shell. trap without any arguments causes it to write a list of signals and their associated action to the standard output, in a format that is suitable as an input to the shell that achieves the same trapping results. very meta of it ✨

Examples:

trap

List trapped signals and their corresponding action

trap '' INT QUIT tstp 30

Ignore signals INT QUIT TSTP USR1

trap date INT

Print date upon receiving signal INT

🌈 type [name ...] 🌈

Interpret each name as a command and print the resolution of the command search. Possible resolutions are: shell keyword, alias, shell builtin, command, tracked alias and not found. For aliases the alias expansion is printed; for commands and tracked aliases the complete pathname of the command is printed. it's literally the "so what ARE you" command and honestly same 🎀

ulimit [-H | -S] [-a | -tfdscmlpnvwr [value]]

ulimit 💅

Bestie this one is literally the process-limit queen. You can peek at or set the hard or soft limits on processes, or set brand new ones. Here's the tea on hard vs soft:

  • the hard limit — no process is allowed to violate it, and once it's been lowered, it may not be raised back up. it's giving final boss energy 🔥
  • the soft limit — processes get signaled when they hit it, but not necessarily killed, and it may be raised ✨

Which one you're playing with is decided by these flags:

  • -H — set or inquire about hard limits
  • -S — set or inquire about soft limits. If neither -H nor -S is specified, the soft limit gets displayed, or both limits get set. If both are specified, the last one wins 👑

Then, which limit you actually want to interrogate or set is chosen by specifying any one of these flags:

  • -a — show all the current limits
  • -t — show or set the limit on CPU time (in seconds)
  • -f — show or set the limit on the largest file that can be created (in 512-byte blocks)
  • -d — show or set the limit on the data segment size of a process (in kilobytes)
  • -s — show or set the limit on the stack size of a process (in kilobytes)
  • -c — show or set the limit on the largest core dump size that can be produced (in 512-byte blocks)
  • -m — show or set the limit on the total physical memory that can be in use by a process (in kilobytes)
  • -l — show or set the limit on how much memory a process can lock with mlock(2) (in kilobytes)
  • -p — show or set the limit on the number of processes this user can have at one time
  • -n — show or set the limit on the number files a process can have open at once
  • -v — show or set the limit on the total virtual memory that can be in use by a process (in kilobytes)
  • -w — show or set the limit on the total number of locks held by a process
  • -r — show or set the limit on the real-time scheduling priority of a process

If you don't specify any of those, it's the limit on file size that gets shown or set. If value is given, the limit gets set to that number; otherwise the current limit just gets displayed. And the special value unlimited represents the lack of any limit — the limitless fantasy, no cap, fr fr 🌈

Limits of an arbitrary process can be displayed or set using the sysctl(8) utility.

umask [mask]

Sets the value of umask (peep umask(2)) to the specified octal value. If you leave the argument out, the current umask value just gets printed at you. 🎀

unalias [-a] [name]

If name is specified, the shell removes that alias. If -a is specified, all aliases get removed — total alias cleanse, so satisfying ✨

unset [-fv] name ...

The specified variables and functions get unset and unexported. If -f or -v is specified, the corresponding function or variable gets unset, respectively. And heads up: if a given name corresponds to both a variable and a function, and you give no options, only the variable gets unset. 😭

wait [job]

Waits for the specified job to complete, then returns the exit status of the last process in the job. If you leave the argument out, it waits for all jobs to complete and returns an exit status of zero. patient queen 💜

🦋 Command Line Editing 🦋

When dash is being used interactively from a terminal, the current command and the command history (see fc in “Builtins”) can be edited using vi-mode command-line editing. This mode uses commands, described below, similar to a subset of those described in the vi man page. The command set -o vi enables vi-mode editing and places sh into vi insert mode. With vi-mode enabled, sh can be switched between insert mode and command mode. It is similar to vi: typing ⟨ESC⟩ enters vi command mode. Hitting ⟨return⟩ while in command mode will pass the line to the shell. iykyk 💅

🫶 EXIT STATUS 🫶

Errors that are detected by the shell — like a syntax error — will cause the shell to exit with a non-zero exit status. If the shell is not an interactive shell, the execution of the shell file will be aborted. Otherwise the shell will return the exit status of the last command executed, or, if the exit builtin is used with a numeric argument, it will return that argument. periodt. 💖

🌸 ENVIRONMENT 🌸

  • HOME — Set automatically by login(1) from the user's login directory in the password file (passwd(4)). This environment variable also functions as the default argument for the cd builtin.
  • PATH — The default search path for executables. See the above section “Path Search”.
  • CDPATH — The search path used with the cd builtin.
  • MAIL — The name of a mail file, that will be checked for the arrival of new mail. Overridden by MAILPATH.
  • MAILCHECK — The frequency in seconds that the shell checks for the arrival of mail in the files specified by the MAILPATH or the MAIL file. If set to 0, the check will occur at each prompt.
  • MAILPATH — A colon : separated list of file names, for the shell to check for incoming mail. This environment setting overrides the MAIL setting. There is a maximum of 10 mailboxes that can be monitored at once.
  • PS1 — The primary prompt string, which defaults to $ , unless you are the superuser, in which case it defaults to # .
  • PS2 — The secondary prompt string, which defaults to > .
  • PS4 — Output before each line when execution trace (set -x) is enabled, defaults to + .
  • IFS — Input Field Separators. This is normally set to ⟨space⟩, ⟨tab⟩, and ⟨newline⟩. See the “White Space Splitting” section for more details.
  • TERM — The default terminal setting for the shell. This is inherited by children of the shell, and is used in the history editing modes.
  • HISTSIZE — The number of lines in the history buffer for the shell.
  • PWD — The logical value of the current working directory. This is set by the cd command.
  • OLDPWD — The previous logical value of the current working directory. This is set by the cd command.
  • PPID — The process ID of the parent process of the shell.

🎀 FILES 🎀

  • $HOME/.profile
  • /etc/profile

⭐ SEE ALSO ⭐

csh(1), echo(1), getopt(1), ksh(1), login(1), printf(1), test(1), getopt(3), passwd(5), environ(7), sysctl(8)

👑 HISTORY 👑

dash is a POSIX-compliant implementation of /bin/sh that aims to be as small as possible. dash is a direct descendant of the NetBSD version of ash (the Almquist SHell), ported to Linux in early 1997. It was renamed to dash in 2002. glow-up timeline honestly 🦋

💀 BUGS 💀

Setuid shell scripts should be avoided at all costs, as they are a significant security risk. not me begging you to not do this 🙈

and that's the whole page bestie!! this one's from the Debian crew, dated January 19, 2003, and it lives in section DASH(1) of the manual 💖 go forth and slay your shell scripts, mwah 🫶✨

📦 where this page comes from