ORIGINAL-AWK(1)

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version 2025-12-25 · 3 versions
, in debian trixie, ubuntu noble, ubuntu questing, ubuntu resolute, ubuntu stonking

💖 ORIGINAL-AWK(1) — the general commands manual page, but make it a vibe 💖

okay bestie, so the manual name is original-awk and it lives in the General Commands Manual section, and honestly? it's a whole legend. let's get into it 🦋

✨ NAME ✨

original-awk — pattern-directed scanning and processing language

like… it scans, it processes, it does the most 💅

✨ SYNOPSIS ✨

original-awk [ -F fs | --csv ] [ -v var=value ] [ 'prog' | -f progfile ]
[ file ...  ]

that's the whole entrance. iconic. no notes. 👑

✨ DESCRIPTION ✨

Awk (the one and only original-awk) goes through every input file looking for lines that match any of a set of patterns — and those patterns are either written literally in prog, or dropped into one or more files you hand over with -f progfile. For every pattern there can be an action attached, and that action runs when a line of a file matches the pattern. 🎯

Each line gets matched against the pattern part of every pattern-action statement, and the associated action runs for each pattern that matched. No skipping, no shortcuts, we're thorough in this house.

The file name - means the standard input. periodt. 🫶

Any file of the form var=value is treated as an assignment, not a filename, and it's executed at the time it would have been opened if it were a filename. Sneaky? A little. Correct? Absolutely.

The option -v followed by var=value is an assignment that happens before prog is executed, and you can have any number of -v options chilling in there.

The -F fs option defines the input field separator to be the regular expression fs.

The --csv option causes awk to process records using (more or less) standard comma-separated values (CSV) format. it's giving spreadsheet energy 📊

An input line is normally made up of fields separated by white space, or by the regular expression FS. The fields are denoted $1, $2, ..., while $0 refers to the entire line. And if FS is null? The input line gets split into one field per character. every single character is a field, bestie, it's a whole situation. 💀

A pattern-action statement has the form:

pattern { action }

A missing { action } means print the line. A missing pattern always matches. And pattern-action statements are separated by newlines or semicolons.

An action is a sequence of statements. A statement can be one of the following:

if( expression ) statement [ else statement ]
while( expression ) statement
for( expression ; expression ; expression ) statement
for( var in array ) statement
do statement while( expression )
break
continue
{ [ statement ... ] }
expression              # commonly var = expression
print [ expression-list ] [ > expression ]
printf format [ , expression-list ] [ > expression ]
return [ expression ]
next                    # skip remaining patterns on this input line
nextfile                # skip rest of this file, open next, start at top
delete array[ expression ]# delete an array element
delete array            # delete all elements of array
exit [ expression ]     # exit immediately; status is expression

Statements are terminated by semicolons, newlines or right braces. An empty expression-list stands for $0. String constants are quoted " ", with the usual C escapes recognized within.

Expressions take on string or numeric values as appropriate, and are built using the operators + - * / % ^ (exponentiation), and concatenation (indicated by white space). The operators ! ++ -- += -= *= /= %= ^= > >= < <= == != ?: are also available in expressions.

Variables may be scalars, array elements (denoted x[i]) or fields. Variables are initialized to the null string. Array subscripts may be any string, not necessarily numeric — this allows for a form of associative memory, which is honestly so iconic of it. 🧠✨ Multiple subscripts such as [i,j,k] are permitted; the constituents are concatenated, separated by the value of SUBSEP.

The print statement prints its arguments on the standard output (or on a file if > file or >> file is present, or on a pipe if | cmd is present), separated by the current output field separator, and terminated by the output record separator. file and cmd may be literal names or parenthesized expressions; identical string values in different statements denote the same open file.

The printf statement formats its expression list according to the format (see printf(3)).

The built-in function close(expr) closes the file or pipe expr. The built-in function fflush(expr) flushes any buffered output for the file or pipe expr.

The mathematical functions atan2, cos, exp, log, sin, and sqrt are built in. Other built-in functions:

  • length([v]) — the length of its argument taken as a string, number of elements in an array for an array argument, or length of $0 if no argument.
  • rand() — random number on [0,1).
  • srand([s]) — sets seed for rand and returns the previous seed.
  • int(x) — truncates to an integer value.
  • substr(s, m [, n]) — the n-character substring of s that begins at position m counted from 1. If no n, use the rest of the string.
  • index(s, t) — the position in s where the string t occurs, or 0 if it does not.
  • match(s, r) — the position in s where the regular expression r occurs, or 0 if it does not. The variables RSTART and RLENGTH are set to the position and length of the matched string.
  • split(s, a [, fs]) — splits the string s into array elements a[1], a[2], ..., a[n], and returns n. The separation is done with the regular expression fs or with the field separator FS if fs is not given. An empty string as field separator splits the string into one array element per character.
  • sub(r, t [, s]) — substitutes t for the first occurrence of the regular expression r in the string s. If s is not given, $0 is used.
  • gsub(r, t [, s]) — same as sub except that all occurrences of the regular expression are replaced; sub and gsub return the number of replacements.
  • sprintf(fmt, expr, ...) — the string resulting from formatting expr ... according to the printf(3) format fmt.
  • system(cmd) — executes cmd and returns its exit status. This will be -1 upon error, cmd's exit status upon a normal exit, 256 + sig upon death-by-signal, where sig is the number of the murdering signal, or 512 + sig if there was a core dump. (yes it really says "murdering signal", we don't make the rules 😭)
  • tolower(str) — returns a copy of str with all upper-case characters translated to their corresponding lower-case equivalents.
  • toupper(str) — returns a copy of str with all lower-case characters translated to their corresponding upper-case equivalents.

The ``function'' getline sets $0 to the next input record from the current input file; getline < file sets $0 to the next record from file. getline x sets variable x instead. Finally, cmd | getline pipes the output of cmd into getline; each call of getline returns the next line of output from cmd.

In all cases, getline returns 1 for a successful input, 0 for end of file, and -1 for an error. those three little numbers are carrying so much weight ngl. 🫡

Patterns are arbitrary Boolean combinations (with ! || &&) of regular expressions and relational expressions. Regular expressions are as in egrep; see grep(1). Isolated regular expressions in a pattern apply to the entire line. Regular expressions may also occur in relational expressions, using the operators ~ and !~. /re/ is a constant regular expression; any string (constant or variable) may be used as a regular expression, except in the position of an isolated regular expression in a pattern. 🚫

A pattern may consist of two patterns separated by a comma; in this case, the action is performed for all lines from an occurrence of the first pattern through an occurrence of the second, inclusive.

A relational expression is one of the following:

expression matchop regular-expression
expression relop expression
expression in array-name
(expr,expr,...) in array-name

where a relop is any of the six relational operators in C, and a matchop is either ~ (matches) or !~ (does not match). A conditional is an arithmetic expression, a relational expression, or a Boolean combination of these.

The special patterns BEGIN and END may be used to capture control before the first input line is read and after the last. BEGIN and END do not combine with other patterns. They may appear multiple times in a program and execute in the order they are read by awk. 🎬

Variable names with special meanings — the VIP list fr:

  • ARGC — argument count, assignable.
  • ARGV — argument array, assignable; non-null members are taken as filenames.
  • CONVFMT — conversion format used when converting numbers (default %.6g).
  • ENVIRON — array of environment variables; subscripts are names.
  • FILENAME — the name of the current input file.
  • FNR — ordinal number of the current record in the current file.
  • FS — regular expression used to separate fields; also settable by option -Ffs.
  • NF — number of fields in the current record.
  • NR — ordinal number of the current record.
  • OFMT — output format for numbers (default %.6g).
  • OFS — output field separator (default space).
  • ORS — output record separator (default newline).
  • RLENGTH — the length of a string matched by match.
  • RSTART — the start position of a string matched by match.
  • RS — input record separator (default newline). If empty, blank lines separate records. If more than one character long, RS is treated as a regular expression, and records are separated by text matching the expression.
  • SUBSEP — separates multiple subscripts (default 034).

Functions may be defined (at the position of a pattern-action statement) thus:

function foo(a, b, c) { ... }

Parameters are passed by value if scalar and by reference if array name; functions may be called recursively. Parameters are local to the function; all other variables are global. Thus local variables may be created by providing excess parameters in the function definition. hack? no. feature. 💅

✨ ENVIRONMENT VARIABLES ✨

If POSIXLY_CORRECT is set in the environment, then awk follows the POSIX rules for sub and gsub with respect to consecutive backslashes and ampersands. 🌈

✨ EXAMPLES ✨

These are verbatim, bestie, don't touch the code.

length($0) > 72 Print lines longer than 72 characters.

{ print $2, $1 } Print first two fields in opposite order.

BEGIN { FS = ",[ \t]*|[ \t]+" }
      { print $2, $1 }

Same, with input fields separated by comma and/or spaces and tabs.

     { s += $1 }
END  { print "sum is", s, " average is", s/NR }

Add up first column, print sum and average.

/start/, /stop/ Print all lines between start/stop pairs.

BEGIN     {    # Simulate echo(1)
     for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
     printf "\n"
     exit }

✨ SEE ALSO ✨

grep(1), lex(1), sed(1)

A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming Language, Second Edition, Addison-Wesley, 2024. ISBN 978-0-13-826972-2, 0-13-826972-6. 📚✨

(part 1 done, more coming bestie — don't go anywhere 💜)

🐛 BUGS 🐛

okay bestie, confession time, nothing's perfect and this page is gonna be honest with you 💖

  • there are literally no explicit conversions between numbers and strings. none. zero. awk is just gonna vibe and hope for the best. so if you need an expression to be treated as a number, you add 0 to it. and if you need it treated as a string, you concatenate "" to it. that's the whole trick, that's the move, iykyk ✨
  • the scope rules for variables inside functions? a botch. like, genuinely. and the syntax for it is even worse. no cap. 😭
  • input is expected to be UTF-8 encoded. other multibyte character sets are simply not handled, sorry babe. however — and this is the plot twist 🎀 — in eight-bit locales, awk treats each input byte as a separate character. so like, one byte = one character. that's the vibe in that specific situation.

🌊 UNUSUAL FLOATING-POINT VALUES 🌊

so here's the lore 📜 awk was designed before IEEE 754 arithmetic went and defined Not-A-Number (NaN) and Infinity values. and those are supported by, like, all modern floating-point hardware now. awk is old. awk is an icon. awk predates the drama. 💅

because awk uses strtod(3) and atof(3) to convert string values into double-precision floating-point values, modern C libraries also convert strings starting with inf and nan into infinity and NaN values respectively. which led to some truly cursed results, like this absolute chaos:

echo nancy | awk '{ print $1 + 0 }'

which prints nan instead of zero. 😭😭 bestie. her name is nancy. she is not a number. but the computer said she was. strange results indeed.

so awk now follows GNU AWK, and it prefilters string values before even attempting to convert them to numbers. here's how that goes down 👇

Hexadecimal values

hexadecimal values (allowed since C99) convert to zero, exactly like they did prior to C99. we're going back to the old ways on this one, periodt. ✨

NaN values

only the two strings +nan and -nan (case independent) convert to NaN. no others do. and yes, NaNs can have signs, that's just how they are. 🤷‍♀️

Infinity values

only the two strings +inf and -inf (case independent) convert to positive and negative infinity, respectively. no others do. that's the whole list, don't try to sneak anything else in there 🙈

and that's a wrap on ORIGINAL-AWK(1) 🫶 this page comes to you from the source/version and date noted in the footer down at the bottom, so go give it a lil kiss goodbye, she's been through a lot 💖✨🎀

📦 where this page comes from