awk [ -F re ] [parameter ... ] [ 'prog' ] [ -fprogfile ] [file ... ]
Description
The -F re option defines the input field separator to be the regular expression reo
Parameters, in the form X= ... y= ... may be passed to awk, where x and yare awk built-in variables (see list below).
awk scans each input file for lines that match any of a set of patterns specified in prog. The prog string must be enclosed in single quotes (') to protect it from the shell. For each pattern in prog there may be an associated action performed when a line of a file matches the pat-tern. The set of pattern-action statements may appear literally as prog or in a file specified with the -f progfile option.
Input files are read in order; if there are no files, the standard input is read. The file name - means the standard input. Each input line is matched against the pattern portion of every pattern-action statement;
the associated action is performed for each matched pattern.
An input line is normally made up of fields separated by white space.
(This default can be changed by using the FS built-invariable or the -F re option.) The fields are denoted $1, $2, ... ; $0 refers to the entire
line. '
A pattern-action statement has the form:
pattern { action }
Either pattern or action may be omitted. If there is no action with a pattern, the matching line is printed. If there is no pattern with an action, the action is performed on every input line.
Patterns are arbitrary Boolean combinations ( !,
I I,'
&&, and parentheses) of rational expressions and regular expressions. Arela-March 15, 1989 AWK-1
AWK (C) AWK (C) tional expression is one of the following:
expression relop expression
expression matchop regular expression
where a relop is any of the six relational operators in C, and a matchop is either - (contains) or ! - (does not contain). A conditional is an arithmetic expression, a relational expression, the special expression
var in array,
or a Boolean combination of these.
The special patterns BEGIN and END may be used to capture control before the first input line has been read and after the last input line has been read respectively. lines between an occurrence of the first pattern and next occurrence of the second pattern.
A regular expression may be used to separate fields by using the -F re option or by assigning the expression to the built-in variable FS . The default is to ignore leading blanks and to separate fields by blanks and/or tab characters. However, if FS is assigned a value, leading blanks are no longer ignored.
Other built-in variables include:
ARGC name of the current input file
ordinal number of the current record in the current file input field separator regular expression (default blank) number of fields in the current record
ordinal number of the current record output format for numbers (default %.6g) output field separator (default blank) output record separator (default new-line) input record separator (default new-line)
AWK-2
AWK (C) AWK (C)
expression # commonly variable
=
expression print [ expression-list ] [ >expression ]printf format [ , expression-list ] [ >expression ] next # skip remaining patterns on this input line exit [expr] # skip the rest of the input; exit status is expr return [expr]
Statements are terminated by semicolons, new lines, or right braces.
An empty expression-list stands for the whole input line. Expressions take on string or numeric values as appropriate, and are built using the operators +, ., *, /, %, and concatenation (indicated by a blank). The C operators ++, --, +=, -=, *=, /=, and %= are also available in expressions. Variables may be scalars, array elements (denoted xli]), or fields. Variables are initialized to the null string or zero. Array subscripts may be any string, not necessarily numeric; this allows for a form of associative memory. String constants are quoted (").
The print statement prints its arguments on the standard output, or on a file if >expression is present, or on a pipe if
I
cmd is present. The arguments are separated by the current output field separator and ter-minated by the output record separator. The printf statement formats its expression list according to the format (see printf(S) in theThe string functions are:
gsub(for, repl, in)
March 15, 1989
behaves like sub (see below), except that it replaces successive occurrences of the regular expression (like the ed global substitute command).
AWK-3
AWK (C)
returns the length of its argument taken as a string, or of the whole line if there is no argument.
returns the position in string s where the regular expression re occurs, or 0 if it does not occur at all.
RSTART is set to the starting position (which is the same as the returned value), and RLENGTH is set to the length of the matched string.
splits the string s into array elements a[1], a[2], a[n], and returns n. The separation is done with the regu-lar expressionfs or with the field separator FS if fs is not given.
sprintfifmt, expr, expr, ... )
formats the expressions according to the printf(S) format given by fmt and returns the resulting string.
sub(for, repl, in) substitutes the string repl in place of the first instance of the regular expression for in string in and returns the number of substitutions. If in is omitted, awk substitutes in the current record ($0).
substr(s, m, n) returns the n-character substring of s that begins at position m.
The input/output and general functions are:
close(jilename) closes the file or pipe named filename.
cmd/getline
sets $0 to the next input record from the current input file.
sets $0 to the next record fromfile.
sets variable var instead.
getline var <file sets var from the next record offile.
system( cmd) executes cmd and returns to its. exit status.
All forms of getline return I for successful input, 0 for end of file, and -1 for an error.
March 15, 1989 AWK-4
AWK (C) AWK (C) awk also provides user-defined functions. Such functions may be defined (in the pattern position of a pattern-action statement) as
function name(args, ... ) { stmts } func name(args, ... ) { stmts }
Function arguments are passed by value if scalar and by reference if array name. Argument names are local to the function; all other vari-able names are global. Function calls may be nested and functions may be recursive. The return statement may be used to return a value.
Examples
Print lines longer than 72 characters:
length > 72
Print first two fields in opposite order:
{ print $2, $1 }
Same, with input fields separated by comma and/or blanks and tabs:
BEGIN { FS = ", [ \t]*[ \t]+" } { print $2, $1 }
Add up the first column, print sum and average:
{ s += $1 }
END { print "sum is", s , " average is", S/NR }
Print fields in reverse order:
{ for (i = NF; i > 0; --i) print $i }
Print all lines between start/stop pairs:
/start/ i /stop/
Print all lines whose first field is different from previous one:
$1 != prev { print; prev = $1 }
March 15, 1989 AWK-5
AWK (C)
Simulate echo(C):
BEGIN
for (i = 1; i < ARGC; i++) printf "%s", ARGV[i]
printf "\n"
exit }
Print file, filling in page numbers starting at 5:
/Page/ {$2 = n++; } { print }
command line: awk -f program n=5 input
See Also
grep(C), sed(C), lex(CP), printf(S)
Notes
AWK (C)
Input white space is not preserved on output if fields are involved.
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 the null string (" ") to it.
Standards Conformance
awk is conformant with:
AT&T SVID Issue 2, Select Code 307-127;
and The X/Open Portability Guide II of January 1987.
March 15, 1989 AWK-6
BANNER (C)