AWK - Basic Syntax

AWK is simple to use and we can provide AWK commands either directly from command line or in the form of a text file having AWK commands. This tutorial explain these two ways of invoking AWK with suitable examples:

AWK Command Line

Following is the form where we can specify AWK command within single quotes at command line itself:

awk [options] file ...

Example

Consider we have a text file marks.txt to be processed and it has following content:

1)    Amit     Physics    80
2)    Rahul    Maths      90
3)    Shyam    Biology    87
4)    Kedar    English    85
5)    Hari     History    89

Let's display complete content of the file using AWK as follows:

[jerry]$ awk '{print}' marks.txt 

On executing the above code, you get the following result:

1)    Amit     Physics    80
2)    Rahul    Maths      90
3)    Shyam    Biology    87
4)    Kedar    English    85
5)    Hari     History    89

AWK Program File

Following is the second form where we can provide AWK commands in a script file:

awk [options] -f file ....

First, create a text command.awk file containing AWK command as shown below:

{print}

Now we can instruct the AWK to read commands from the text file and perform the action. Here, we achieve the same result as shown in the above example.

[jerry]$ awk -f command.awk marks.txt

On executing the above code, you get the following result:

1)    Amit     Physics    80
2)    Rahul    Maths      90
3)    Shyam    Biology    87
4)    Kedar    English    85
5)    Hari     History    89

AWK Standard Options

AWK supports the following standard options which can be provided from command line.

The -v option

This option assigns a value to variable. It allows assignment before the program execution. Below simple example describes the usage of the -v option.

[jerry]$ awk -v name=Jerry 'BEGIN{printf "Name = %s\n", name}'

On executing the above code, you get the following result:

Name = Jerry

The --dump-variables[=file] option

It prints a sorted list of global variables and their final values to file. The default file is awkvars.out.

[jerry]$ awk --dump-variables ''
[jerry]$ cat awkvars.out 

On executing the above code, you get the following result:

ARGC: 1
ARGIND: 0
ARGV: array, 1 elements
BINMODE: 0
CONVFMT: "%.6g"
ERRNO: ""
FIELDWIDTHS: ""
FILENAME: ""
FNR: 0
FPAT: "[^[:space:]]+"
FS: " "
IGNORECASE: 0
LINT: 0
NF: 0
NR: 0
OFMT: "%.6g"
OFS: " "
ORS: "\n"
RLENGTH: 0
RS: "\n"
RSTART: 0
RT: ""
SUBSEP: "\034"
TEXTDOMAIN: "messages"

The --help option

This option prints the help message on standard output.

[jerry]$ awk --help

On executing the above code, you get the following result:

Usage: awk [POSIX or GNU style options] -f progfile [--] file ...
Usage: awk [POSIX or GNU style options] [--] 'program' file ...
POSIX options:  GNU long options: (standard)
 -f progfile  --file=progfile
 -F fs   --field-separator=fs
 -v var=val  --assign=var=val
Short options:  GNU long options: (extensions)
 -b   --characters-as-bytes
 -c   --traditional
 -C   --copyright
 -d[file]  --dump-variables[=file]
 -e 'program-text' --source='program-text'
 -E file   --exec=file
 -g   --gen-pot
 -h   --help
 -L [fatal]  --lint[=fatal]
 -n   --non-decimal-data
 -N   --use-lc-numeric
 -O   --optimize
 -p[file]  --profile[=file]
 -P   --posix
 -r   --re-interval
 -S   --sandbox
 -t   --lint-old
 -V   --version

The --lint[=fatal] option

This option enables checking of non-portable or dubious constructs. When an argument fatal is provided, it treats warnings messages as errors. Below simple example illustrates this:

[jerry]$ awk --lint '' /bin/ls

On executing the above code, you get the following result:

awk: cmd. line:1: warning: empty program text on command line
awk: cmd. line:1: warning: source file does not end in newline
awk: warning: no program text at all!

The --posix option

This option turns on strict POSIX compatibility, in which all common and gawk-specific extensions are disabled.

The --profile[=file] option

This option generates a pretty-printed version of the program in file. Default file is awkprof.out. Below simple example illustrates this:

[jerry]$ awk --profile 'BEGIN{printf"---|Header|--\n"} {print} END{printf"---|Footer|---\n"}' marks.txt > /dev/null 
[jerry]$ cat awkprof.out

On executing the above code, you get the following result:

# gawk profile, created Sun Oct 26 19:50:48 2014

 # BEGIN block(s)

 BEGIN {
  printf "---|Header|--\n"
 }

 # Rule(s)

 {
  print $0
 }

 # END block(s)

 END {
  printf "---|Footer|---\n"
 }

The --traditional option

This option disables all gawk-specific extensions.

The --version option

This option displays the version information of the AWK program.

[jerry]$ awk --version

When above code is executed, it will produce following result:

GNU Awk 4.0.1
Copyright (C) 1989, 1991-2012 Free Software Foundation.