AWK - Basic Syntax

AWK is simple to use. We can provide AWK commands either directly from the command line or in the form of a text file containing AWK commands.
We can specify an AWK command within single quotes at command line as shown −
awk [options] file ...

Consider a text file marks.txt with the following content −
1) Amit     Physics    80
2) Rahul    Maths      90
3) Shyam    Biology    87
4) Kedar    English    85
5) Hari     History    89

Let us display the complete content of the file using AWK as follows −
Example
[jerry]$ awk '{print}' marks.txt 
On executing this code, you get the following result −
Output
1) Amit     Physics    80
2) Rahul    Maths      90
3) Shyam    Biology    87
4) Kedar    English    85
5) Hari     History    89

We can provide AWK commands in a script file as shown −
awk [options] -f file ....

First, create a text file command.awk containing the 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.
Example
[jerry]$ awk -f command.awk marks.txt
On executing this code, you get the following result −
Output
1) Amit  Physics 80
2) Rahul Maths   90
3) Shyam Biology 87
4) Kedar English 85
5) Hari  History 89

AWK supports the following standard options which can be provided from the command line.
This option assigns a value to a variable. It allows assignment before the program execution. The following example describes the usage of the -v option.
Example
[jerry]$ awk -v name=Jerry 'BEGIN{printf "Name = %s\n", name}'
On executing this code, you get the following result −
Output
Name = Jerry

It prints a sorted list of global variables and their final values to file. The default file is awkvars.out.
Example
[jerry]$ awk --dump-variables ''
[jerry]$ cat awkvars.out 
On executing the above code, you get the following result −
Output
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"

This option prints the help message on standard output.
Example
[jerry]$ awk --help
On executing this code, you get the following result −
Output
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

This option enables checking of non-portable or dubious constructs. When an argument fatal is provided, it treats warning messages as errors. The following example demonstrates this −
Example
[jerry]$ awk --lint '' /bin/ls
On executing this code, you get the following result −
Output
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!

This option turns on strict POSIX compatibility, in which all common and gawk-specific extensions are disabled.
This option generates a pretty-printed version of the program in file. Default file is awkprof.out. Below simple example illustrates this −
Example
[jerry]$ awk --profile 'BEGIN{printf"---|Header|--\n"} {print} 
END{printf"---|Footer|---\n"}' marks.txt > /dev/null 
[jerry]$ cat awkprof.out
On executing this code, you get the following result −
Output
# 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"
   }

This option disables all gawk-specific extensions.
This option displays the version information of the AWK program.
Example
[jerry]$ awk --version
When this code is executed, it produces the following result −
Output
GNU Awk 4.0.1
Copyright (C) 1989, 1991-2012 Free Software Foundation.

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