Manual Pages for UNIX Darwin command on man awk

AWK(1) AWK(1)

awk

NAME

awk - pattern-directed scanning and processing language

SYNOPSIS

aawwkk [ -FF fs ] [ -vv var=value ] [ 'prog' | -ff progfile ] [ file ... ]

DESCRIPTION

Awk scans each input file for lines that match any of a set of patterns

specified literally in prog or in one or more files specified as -ff

progfile. With each pattern there can be an associated action that will be performed when a line of a file matches the pattern. Each line

is matched against the pattern portion of every pattern-action state-

ment; the associated action is performed for each matched pattern. The

file name - means the standard input. Any file of the form var=value

is treated as an assignment, not a filename, and is executed at the

time it would have been opened if it were a filename. The option -vv

followed by var=value is an assignment to be done before prog is exe-

cuted; any number of -vv options may be present. The -FF fs option

defines the input field separator to be the regular expression fs. An input line is normally made up of fields separated by white space,

or by regular expression FFSS. The fields are denoted $$11, $$22, ..., while

$$00 refers to the entire line. If FFSS is null, the input line is split

into one field per character.

A pattern-action statement has the form

pattern {{ action }} A missing {{ action }} means print the line; a missing pattern always

matches. Pattern-action statements are separated by newlines or semi-

colons. 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 $$00. 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. Multiple subscripts such as [[ii,,jj,,kk]] are permitted; the constituents are concatenated, separated by the value of SSUUBBSSEEPP. The pprriinntt 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 paren-

thesized expressions; identical string values in different statements denote the same open file. The pprriinnttff statement formats its expression

list according to the format (see printf(3)). The built-in function

cclloossee((expr)) closes the file or pipe expr. The built-in function

fffflluusshh((expr)) flushes any buffered output for the file or pipe expr. The mathematical functions eexxpp, lloogg, ssqqrrtt, ssiinn, ccooss, and aattaann22 are

built in. Other built-in functions:

lleennggtthh the length of its argument taken as a string, or of $$00 if no

argument. rraanndd random number on (0,1) ssrraanndd sets seed for rraanndd and returns the previous seed. iinntt truncates to an integer value ssuubbssttrr((s,, m,, n))

the n-character substring of s that begins at position m counted

from 1. iinnddeexx((s,, t)) the position in s where the string t occurs, or 0 if it does not. mmaattcchh((s,, r)) the position in s where the regular expression r occurs, or 0 if it does not. The variables RRSSTTAARRTT and RRLLEENNGGTTHH are set to the position and length of the matched string. sspplliitt((s,, a,, fs)) splits the string s into array elements a[[11]], a[[22]], ..., a[[n]],

and returns n. The separation is done with the regular expres-

sion fs or with the field separator FFSS if fs is not given. An empty string as field separator splits the string into one array element per character. ssuubb((r,, t,, s)) substitutes t for the first occurrence of the regular expression

r in the string s. If s is not given, $$00 is used.

ggssuubb same as ssuubb except that all occurrences of the regular expres-

sion are replaced; ssuubb and ggssuubb return the number of replace-

ments. sspprriinnttff((fmt,, expr,, ... )) the string resulting from formatting expr ... according to the printf(3) format fmt ssyysstteemm((cmd)) executes cmd and returns its exit status ttoolloowweerr((str))

returns a copy of str with all upper-case characters translated

to their corresponding lower-case equivalents.

ttoouuppppeerr((str))

returns a copy of str with all lower-case characters translated

to their corresponding upper-case equivalents.

The ``function'' ggeettlliinnee sets $$00 to the next input record from the cur-

rent input file; ggeettlliinnee < ggeettlliinnee x sets variable x instead. Finally, cmd || ggeettlliinnee pipes the output of cmd into ggeettlliinnee; each call of ggeettlliinnee returns the next line of output from cmd. In all cases, ggeettlliinnee returns 1 for a successful

input, 0 for end of file, and -1 for an error.

Patterns are arbitrary Boolean combinations (with !! |||| &&&&) of regular expressions and relational expressions. Regular expressions are as defined in reformat(7). Isolated regular expressions in a pattern

apply to the entire line. Regular expressions may also occur in rela-

tional 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 though an occurrence of the second. A relational expression is one of the following:

expression matchop regular-expression

expression relop expression

expression iinn array-name

((expr,,expr,...)) iinn 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 combi-

nation of these. The special patterns BBEEGGIINN and EENNDD may be used to capture control before the first input line is read and after the last. BBEEGGIINN and EENNDD do not combine with other patterns. Variable names with special meanings: CCOONNVVFFMMTT

conversion format used when converting numbers (default %%..66gg)

FFSS regular expression used to separate fields; also settable by

option -FFfs.

NNFF number of fields in the current record NNRR ordinal number of the current record FFNNRR ordinal number of the current record in the current file

FILENAME

the name of the current input file RRSS input record separator (default newline) OOFFSS output field separator (default blank) OORRSS output record separator (default newline)

OOFFMMTT output format for numbers (default %%..66gg)

SSUUBBSSEEPP separates multiple subscripts (default 034) AARRGGCC argument count, assignable

AARRGGVV argument array, assignable; non-null members are taken as file-

names EENNVVIIRROONN array of environment variables; subscripts are names.

Functions may be defined (at the position of a pattern-action state-

ment) thus: ffuunnccttiioonn ffoooo((aa,, bb,, cc)) {{ ......;; rreettuurrnn xx }} 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. EEXXAAMMPPLLEESS

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 blanks 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 }

BUGS

There are no explicit conversions between numbers and strings. To force an expression to be treated as a number add 0 to it; to force it to be treated as a string concatenate "" to it. The scope rules for variables in functions are a botch; the syntax is worse. AWK(1)