AWK

pattern-directed scanning and processing language

awk [-v var=value[…]] [-F fs ] [prog | -f progFile … ] [- | inputFile [ var=value] … ]

Scans each inputFile for lines that match any of a set of patterns (or all lines if no pattern in prog or -f progFile.

With each pattern there may be an action to be performed when a line matches .


`-v` `var=value`	Assignment statments executed before `prog` is started. Any number of `-v`s may be used.
`-F fs`	Field separator is a regular expression which Splits an input line (`$`0) into fields `$1, $2, …,`. `awkprog.sh "123 aaa 999"` has only 1 field because the default `FS` is if `FS` is null each character is a field.
`-` ^{not ^}	Input from `stdin` instead of `inputFile`
`progFile` or `stdin` (with `-)`	Provides instructions in form : `pattern-action`.

A pattern-action statement has the form:

[pattern] [{ action }]

Omitting the pattern matches all lines.
Omitting the { action } outputs the line.

Patterns

The special patterns BEGIN and END perform actions before the first input line is read and after the last and do not combine with other patterns.

Boolean combinations (with ! || && of regular expressions and relational expressions as in egrep.
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.

For two patterns separated by a comma;
the action is performed for lines from an occurrence of the first pattern though the second.

A relational expression is :

expression matchOp regular-expression expression relOp expression expression in array-name (expr,expr,...) in array-name

matchOp is either ~ (matches) or !~ (does not match).
relOp is any < <= == >= > ! and

A conditional is an arithmetic expression, a relational expression, or a Boolean combination of these.

Actions

action statements are separated by newlines or semi-colons.
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
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
print^† [ expression-list ] [ > expression ]
printf^† format [ , expression-list ] [ > expression ]

An empty expression-list implies $0, that is the entire input line.

Statements are terminated by semicolons, newlines or right braces.
String constants are " quoted ", with escapes being \a, \t, \r, \n, \" , \e , \c and \xXX.
Expressions take on string or numeric values as appropriate and
are built with operators + - * / % ^ (exponentiation) and concatenation (indicated by white space).
To cast a string to a number add 0 to it;
To cast a number to a string concatenate "" to it.

operators: ! ++ -- += -= *= /= %= ^= > > < < == != ?: .
Variables may be scalars, array elements (denoted x[i]) or fields, are initialized to the null.
subscripts may be strings. Multiple subscripts such as [i,j,k] are permitted; the constituents are concatenated, separated by the value of SUBSEP.

print arguments are formatted and output to standard output ( or >file , >> appends to file) separated by OFS(default tab) and terminated by the ORS(default \n(newLine)).
file and cmd may be literal names or parenthesized expressions. Identical string values in different statements denote the same open file.

printf formats its expression list (to add a new line use \n)
The character % is followed by zero or more of the flags defined in the C standard.

#

The value is converted to THE alternate form.

`x` and `X`	0`x` or 0`X` is prepended to non-zero result
`a, A, e, E, f, F, g`, and `G`	always contain a decimal point, even if no digits follow it. normally, a decimal point appears only if a digit follows.
`g` and G	trailing zeros are not removed
`o` (octal)	0 is prepended.
	For other conversions, the result is undefined.

-

value is left adjusted on the field boundary.

Default: right justification

12

rather than on the left with blanks or zeros

12

n pads on the right with blanks

12

0 The value is zero filled.
For d, i, o, u, x, X, a, A, e, E, f, F, g, and G the value is filled on the left with zeros.
If 0 and - are present, 0 is ignored.
If a precision is given with a numeric conversion (d, i, o, u, x, and X), 0 is ignored.

space A blank is placed before a positive number (or empty string) produced by a signed conversion.

+ A sign, + or -, is placed before a number produced by a signed conversion.
A + (plus sign) overrides a space if both are used. Default: a sign is used only for negative numbers.

' For decimal conversion (i, d, u, f, F, g, G) the output is to be grouped with thousands' grouping characters if the locale information provides any.

I For decimal integer conversion (i, d, u) the output uses the locale's alternative output digits.
For example, this will give Arabic-Indic digits in the Persian ('fa_IR') locale.

example: printf "%6d %s", NR, $0

sprintf(fmt, expr, … ) returns the string resulting from formatting
close(expr) closes the file or pipe expr. fflush(expr) flushes buffered output.

exp log sqrt sin cos atan2
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
substr(string,m,n) begins at position m (counted from 1) n^th-character substring of string
index(string,substr) the position in string where substr occurs, or 0 if it does not.
match(string,regex) the position in string where the regular expression regex occurs, or 0 if it does not.
RSTART and RLENGTH are set to the position and length of the matched string.
split(string, array[,fs]) splits string into array elements array[1], array[2], … array[n], and returns ni.
The separation is done with the regular expression fs or with FS if fs is not given or null splits the string into 1 array element per character.

regex in string. $0 is the default for string .
sub(regex,repl[,string]) substitutes repl for the first occurrence of the regular expression
gsub global substituion version of sub
sub and gsub return the number of replacements.

system(cmd) executes cmd and returns its exit status

tolower(str) returns a copy of str with all upper-case characters translated to lower-case .
toupper(str) returns a copy of str with all lower-case characters translated to upper-case .

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 .
N. B. returns 1 for a successfuli input, 0 for end of file, and -1 for an error.

cmd | getline pipes the output of cmd into getline; each call of getline returns the next line of output from cmd.

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

function add3(a, b, c) { x=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; local variables may be created by providing excess parameters in the function definition.
All other variables are global,

Keywords

FILENAME the name of the current input file
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 , across all input files.(i.e. 1,2,3,4 …)
FNR ordinal number of the current record in the current file

input fields are seperated by whitespace.
RS input record separator (default \n)

OFS output field separator (default blank)
ORS output record separator (default \n)
OFMT output format for numbers (default %.6g)

SUBSEP subscript separater (default ,)

ARGC argument count, assignable
ARGV argument array, assignable; non-null members are taken as filenames

ENVIRON array of environment variables; subscripts are names.

Examples

If a line is longer than 80 characters wide; output the record Number, the begining and the end of line

awk '{ if( length > 80 ) print NR,substr($0,1,16), " -- " substr($0,70,100 ); 
else print NR,$0 }" ' /var/log/system.log

638 May  6 13:59:12   -- CaptivePublishState:1211 en1 - PreProbe
639 May  6 13:59:12 smackerPro configd[16]: network configuration changed.
640 May  6 13:59:12   -- fad0a750>: Stream error occurred for : The operation couldn’t be comple
641 May  6 13:59:12   -- fad0a750>: Stream error occurred for : The operation couldn’t be comple

Print first two fields in opposite order.

{ print $2, $1 }

with input fields separated by comma and/or blanks and tabs.

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

              Add up first column, print sum and average.
            { s += $1 }
       END  { print "sum is", s, " average is", s/NR }

Print all lines between start/stop pairs.

 /start/, /stop/

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

#! /usr/bin/awk -f
# select lines where col 5 > 155 and seperate columns with + except field 5 use > <
BEGIN { FS=","}   # set Field Seperator BEFORE starting the program lest the first line use default FS (i.e. white space)

{
if( $5 >155) print NF, $1,"+",$2,"+",$3, "+",$4, ">",$5, "<",$6, "+",$7,"+",$8,"+",$9 
}


#! /usr/bin/awk -f
# output first column left justified and others right justified as in a load map.
{ printf "%-38s %8s %10s %s  %s", $1,$2, $3,$4, "\n" }

echo system up for `uptime --pretty | awk '{ print $2*24+ $4 }'` minutes

Environment Varilables

> LC_ALL=en_US.UTF-8
Causes printf to output numbers values greater than 999 with commas when using ' in the format string.
Note: unset LC_ALL will not add commas!

 >ls -log sheet001.htm
-rw-r--r-- 1 6331 Feb  5 12:55 sheet001.htm

>export LC_ALL=en_US.UTF-8 
>ls -log sheet001.htm|\
>awk '{ printf " %'d \\n", \$3 }'   2>&1
 6,331

Add line number to each line in a file with 2 fields:cat file |awk '{print i++,$1,$2}'

SEE gawk,lex(1), sed(1)