AWK(1) AWK(1)
NAME
awk - pattern-directed scanning and processing language
SYNOPSIS
awk [ -F fs ] [ -d ] [ -mf n ] [ -mr n ] [ -safe ] [ -v
var=value ] [ -f progfile | prog ] [ 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 -f 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 statement; 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 file name,
and is executed at the time it would have been opened if it
were a file name. The option -v followed by var=value is an
assignment to be done before the program is executed; any
number of -v options may be present. -F 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 FS. The fields are
denoted $1, $2, ..., while $0 refers to the entire line. If
FS is null, the input line is split into one field per char-
acter.
To compensate for inadequate implementation of storage man-
agement, the -mr option can be used to set the maximum size
of the input record, and the -mf option to set the maximum
number of fields.
The -safe option causes awk to run in ``safe mode,'' in
which it is not allowed to run shell commands or open files
and the environment is not made available in the ENVIRON
variable.
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 semicolons.
An action is a sequence of statements. A statement can be
one of the following:
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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 recog-
nized 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. Vari-
ables 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
[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 separa-
tor. 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 fprintf(2)).
The built-in function close(expr) closes the file or pipe
expr. The built-in function fflush(expr) flushes any buf-
fered output for the file or pipe expr. If expr is omitted
or is a null string, all open files are flushed.
The mathematical functions exp, log, sqrt, sin, cos, and
atan2 are built in. Other built-in functions:
length If its argument is a string, the string's length is
returned. If its argument is an array, the number
of subscripts in the array is returned. If no
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argument, the length of $0 is returned.
rand random number on (0,1)
srand sets seed for rand and returns the previous seed.
int truncates to an integer value
utf converts its numerical argument, a character number,
to a UTF string
substr(s, m, n)
the n-character substring of s that begins at posi-
tion m counted from 1. If n is omitted, it is taken
to be the length of s from m.
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 regu-
lar expression r in the string s. If s is not given,
$0 is used. A `&' character in t will be replaced
by the sub-string of s matched by r; it may be
escaped with `\' to substitute a literal `&'.
gsub same as sub except that all occurrences of the regu-
lar expression are replaced; sub and gsub return the
number of replacements.
sprintf(fmt, expr, ...)
the string resulting from formatting expr ...
according to the printf format fmt
system(cmd)
executes cmd and returns its exit status
tolower(str)
returns a copy of str with all upper-case characters
translated to their corresponding lower-case equiva-
lents.
toupper(str)
returns a copy of str with all lower-case characters
translated to their corresponding upper-case equiva-
lents.
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;
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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.
Patterns are arbitrary Boolean combinations (with ! || &&)
of regular expressions and relational expressions. Regular
expressions are as in regexp(6). Isolated regular expres-
sions 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 expres-
sion; 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 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.
Variable names with special meanings:
CONVFMT conversion format used when converting numbers
(default %.6g)
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
FNR ordinal number of the current record in the cur-
rent file
FILENAME the name of the current input file
RS input record separator (default newline)
OFS output field separator (default blank)
ORS output record separator (default newline)
OFMT output format for numbers (default %.6g)
SUBSEP separates multiple subscripts (default 034)
ARGC argument count, assignable
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ARGV argument array, assignable; non-null members are
taken as file names
ENVIRON array of environment variables; subscripts are
names.
Functions may be defined (at the position of a pattern-
action statement) thus:
function foo(a, b, c) { ...; return x }
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.
EXAMPLES
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 }
SOURCE
/sys/src/cmd/awk
SEE ALSO
sed(1), regexp(6),
A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Pro-
gramming Language, Addison-Wesley, 1988. ISBN 0-201-07981-X
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
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concatenate "" to it.
The scope rules for variables in functions are a botch; the
syntax is worse.
UTF is not always dealt with correctly, though awk does make
an attempt to do so. The split function with an empty
string as final argument now copes with UTF in the string
being split.
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