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| AWK(1plan9) | AWK(1plan9) |
NAME¶
awk - pattern-directed scanning and processing languageSYNOPSIS¶
awk [ -Ffs ] [ -v var=value ] [ -mrn ] [ -mfn ] [ -f prog [ 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 file. 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 prog 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 character. To compensate for inadequate implementation of storage management, 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. A pattern-action statement has the form- pattern { action }
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.
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 fprintf(2)). 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 exp, log, sqrt, sin,
cos, and atan2 are built in. Other built-in functions:
- length
- the length of its argument taken as a string, or of $0 if no argument.
- 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 position m counted from 1.
- 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
- 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 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 equivalents.
- toupper(str)
- returns a copy of str with all lower-case characters translated to their corresponding upper-case equivalents.
- expression matchop regular-expression
expression relop expressionexpression in array-name(expr,expr,...) in array-name
- 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 current 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
- ARGV
- argument array, assignable; non-null members are taken as file names
- ENVIRON
- array of environment variables; subscripts are names.
- function foo(a, b, c) { ...; return x }
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 }