<!DOCTYPE html><html><body><title>AWK Tutorial</title>

<h1>Awk Tutorial</h1>

<p>This tutorial takes you through AWK, one of the most prominent text-processing utility on GNU/Linux. It is very powerful and uses simple programming language. It can solve complex text processing tasks with a few lines of code. Starting with an overview of AWK, its environment, and workflow, the tutorial proceeds to explain the syntax, variables, operators, arrays, loops, and functions used in AWK. It also covers topics such as output redirection and pretty printing.</p>

<h1>Audience</h1>

<p>This tutorial will be useful for software developers, system administrators, or any enthusiastic reader inclined to learn how to do text processing and data extraction in Unix-like environment.</p>

<h1>Prerequisites</h1>

<p>You must have a basic understanding of GNU/Linux operating system and shell scripting.</p>

<p>&copy; Copyright 2017. All Rights Reserved.</p>

<title>AWK Overview</title>

<h1>AWK - Overview</h1>

<p>AWK is an interpreted programming language. It is very powerful and specially designed for text processing. Its name is derived from the family names of its authors &minus; <b>Alfred Aho, Peter Weinberger, and Brian Kernighan.</b></p>

<p>The version of AWK that GNU/Linux distributes is written and maintained by the Free Software Foundation (FSF); it is often referred to as <b>GNU AWK.</b></p>

<h2>Types of AWK</h2>

<p>Following are the variants of AWK &minus;</p>

<p><b>AWK</b> &minus; Original AWK from AT &amp; T Laboratory.</p>

<p><b>NAWK</b> &minus; Newer and improved version of AWK from AT &amp; T Laboratory.</p>

<p><b>GAWK</b> &minus; It is GNU AWK. All GNU/Linux distributions ship GAWK. It is fully compatible with AWK and NAWK.</p>

<h2>Typical Uses of AWK</h2>

<p>Myriad of tasks can be done with AWK. Listed below are just a few of them &minus;</p>

<p>&copy; Copyright 2017. All Rights Reserved.</p>

<title>AWK Environment</title>

<h1>AWK - Environment</h1>

<p>This chapter describes how to set up the AWK environment on your GNU/Linux system.</p>

<h2>Installation Using Package Manager</h2>

<p>Generally, AWK is available by default on most GNU/Linux distributions. You can use <b>which</b> command to check whether it is present on your system or not. In case you don’t have AWK, then install it on Debian based GNU/Linux using Advance Package Tool <b>(APT)</b> package manager as follows &minus;</p>

<p>Similarly, to install AWK on RPM based GNU/Linux, use Yellowdog Updator Modifier <b>yum</b> package manager as follows &minus;</p>

<p>After installation, ensure that AWK is accessible via command line.</p>

<p>On executing the above code, you get the following result &minus;</p>

<h2>Installation from Source Code</h2>

<p>As GNU AWK is a part of the GNU project, its source code is available for free download. We have already seen how to install AWK using package manager. Let us now understand how to install AWK from its source code.</p>

<p>The following installation is applicable to any GNU/Linux software, and for most other freely-available programs as well. Here are the installation steps &minus;</p>

<p><b>Step 1</b> &minus; Download the source code from an authentic place. The command-line utility <b>wget</b> serves this purpose.</p>

<p><b>Step 2</b> &minus; Decompress and extract the downloaded source code.</p>

<p><b>Step 3</b> &minus; Change into the directory and run configure.</p>

<p><b>Step 4</b> &minus; Upon successful completion, the <b>configure</b> generates Makefile. To compile the source code, issue a <b>make</b> command.</p>

<p><b>Step 5</b> &minus; You can run the test suite to ensure the build is clean. This is an optional step.</p>

<p><b>Step 6</b> &minus; Finally, install AWK. Make sure you have super-user privileges.</p>

<p>That is it! You have successfully compiled and installed AWK. Verify it by executing the <b>awk</b> command as follows &minus;</p>

<p>On executing this code, you get the following result &minus;</p>

<p>&copy; Copyright 2017. All Rights Reserved.</p>

<pre class="prettyprint notranslate">

[jeryy]$ sudo apt-get update

[jeryy]$ sudo apt-get install gawk

<p>Similarly, to install AWK on RPM based GNU/Linux, use Yellowdog Updator Modifier <b>yum</b> package manager as follows &minus;</p>

<pre class="prettyprint notranslate">

[root]# yum install gawk

<p>After installation, ensure that AWK is accessible via command line.</p>

<pre class="prettyprint notranslate">

[jerry]$ which awk

<p>On executing the above code, you get the following result &minus;</p>

<pre class="result notranslate">

/usr/bin/awk

<h2>Installation from Source Code</h2>

<p>As GNU AWK is a part of the GNU project, its source code is available for free download. We have already seen how to install AWK using package manager. Let us now understand how to install AWK from its source code.</p>

<p>The following installation is applicable to any GNU/Linux software, and for most other freely-available programs as well. Here are the installation steps &minus;</p>

<p><b>Step 1</b> &minus; Download the source code from an authentic place. The command-line utility <b>wget</b> serves this purpose.</p>

<pre class="prettyprint notranslate">

[jerry]$ wget http://ftp.gnu.org/gnu/gawk/gawk-4.1.1.tar.xz

<p><b>Step 2</b> &minus; Decompress and extract the downloaded source code.</p>

<pre class="prettyprint notranslate">

[jerry]$ tar xvf gawk-4.1.1.tar.xz

<p><b>Step 3</b> &minus; Change into the directory and run configure.</p>

<pre class="prettyprint notranslate">

[jerry]$ ./configure

<p><b>Step 4</b> &minus; Upon successful completion, the <b>configure</b> generates Makefile. To compile the source code, issue a <b>make</b> command.</p>

<pre class="prettyprint notranslate">

[jerry]$ make

<p><b>Step 5</b> &minus; You can run the test suite to ensure the build is clean. This is an optional step.</p>

<pre class="prettyprint notranslate">

[jerry]$ make check

<p><b>Step 6</b> &minus; Finally, install AWK. Make sure you have super-user privileges.</p>

<pre class="prettyprint notranslate">

[jerry]$ sudo make install

<p>That is it! You have successfully compiled and installed AWK. Verify it by executing the <b>awk</b> command as follows &minus;</p>

<pre class="prettyprint notranslate">

[jerry]$ which awk

<p>On executing this code, you get the following result &minus;</p>

<pre class="result notranslate">

/usr/bin/awk

<title>AWK Workflow</title>

<h1>AWK - Workflow</h1>

<p>To become an expert AWK programmer, you need to know its internals. AWK follows a simple workflow &minus; Read, Execute, and Repeat. The following diagram depicts the workflow of AWK &minus;</p>

<h3>Read</h3>

<p>AWK reads a line from the input stream (file, pipe, or stdin) and stores it in memory.</p>

<h3>Execute</h3>

<p>All AWK commands are applied sequentially on the input. By default AWK execute commands on every line. We can restrict this by providing patterns.</p>

<h3>Repeat</h3>

<p>This process repeats until the file reaches its end.</p>

<h2>Program Structure</h2>

<p>Let us now understand the program structure of AWK.</p>

<h3>BEGIN block</h3>

<p>The syntax of the BEGIN block is as follows &minus;</p>

<p><b>Syntax</b></p>

<p>The BEGIN block gets executed at program start-up. It executes only once. This is good place to initialize variables. BEGIN is an AWK keyword and hence it must be in upper-case. Please note that this block is optional.</p>

<h3>Body Block</h3>

<p>The syntax of the body block is as follows &minus;</p>

<p><b>Syntax</b></p>

<p>The body block applies AWK commands on every input line. By default, AWK executes commands on every line. We can restrict this by providing patterns. Note that there are no keywords for the Body block.</p>

<h3>END Block</h3>

<p>The syntax of the END block is as follows &minus;</p>

<p><b>Syntax</b></p>

<p>The END block executes at the end of the program. END is an AWK keyword and hence it must be in upper-case. Please note that this block is optional.</p>

<p>Let us create a file <b>marks.txt</b> which contains the serial number, name of the student, subject name, and number of marks obtained.</p>

<p>Let us now display the file contents with header by using AWK script.</p>

<p><b>Example</b></p>

<p>When this code is executed, it produces the following result &minus;</p>

<p><b>Output</b></p>

<p>At the start, AWK prints the header from the BEGIN block. Then in the body block, it reads a line from a file and executes AWK's print command which just prints the contents on the standard output stream. This process repeats until file reaches the end.</p>

<p>&copy; Copyright 2017. All Rights Reserved.</p>

<pre class="result notranslate">

BEGIN {awk-commands}

<p>The BEGIN block gets executed at program start-up. It executes only once. This is good place to initialize variables. BEGIN is an AWK keyword and hence it must be in upper-case. Please note that this block is optional.</p>

<h3>Body Block</h3>

<p>The syntax of the body block is as follows &minus;</p>

<p><b>Syntax</b></p>

<pre class="result notranslate">

/pattern/ {awk-commands}

<p>The body block applies AWK commands on every input line. By default, AWK executes commands on every line. We can restrict this by providing patterns. Note that there are no keywords for the Body block.</p>

<h3>END Block</h3>

<p>The syntax of the END block is as follows &minus;</p>

<p><b>Syntax</b></p>

<pre class="result notranslate">

END {awk-commands}

<p>The END block executes at the end of the program. END is an AWK keyword and hence it must be in upper-case. Please note that this block is optional.</p>

<p>Let us create a file <b>marks.txt</b> which contains the serial number, name of the student, subject name, and number of marks obtained.</p>

<pre class="result notranslate">

1) Amit Physics 80

2) Rahul Maths 90

3) Shyam Biology 87

4) Kedar English 85

5) Hari History 89

<p>Let us now display the file contents with header by using AWK script.</p>

<p><b>Example</b></p>

<pre class="prettyprint notranslate">

[jerry]$ awk 'BEGIN{printf "Sr No\tName\tSub\tMarks\n"} {print}' marks.txt

<p>When this code is executed, it produces the following result &minus;</p>

<p><b>Output</b></p>

<pre class="result notranslate">

Sr No Name Sub Marks

1) Amit Physics 80

2) Rahul Maths 90

3) Shyam Biology 87

4) Kedar English 85

5) Hari History 89

<title>AWK Basic Syntax</title>

<h1>AWK - Basic Syntax</h1>

<p>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.</p>

<h2>AWK Command Line</h2>

<p>We can specify an AWK command within single quotes at command line as shown &minus;</p>

<h3>Example</h3>

<p>Consider a text file <b>marks.txt</b> with the following content &minus;</p>

<p>Let us display the complete content of the file using AWK as follows &minus;</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h2>AWK Program File</h2>

<p>We can provide AWK commands in a script file as shown &minus;</p>

<p>First, create a text file <b>command.awk</b> containing the AWK command as shown below &minus;</p>

<p>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.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h2>AWK Standard Options</h2>

<p>AWK supports the following standard options which can be provided from the command line.</p>

<h3>The -v option</h3>

<p>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.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>The --dump-variables[=file] option</h3>

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

<p><b>Example</b></p>

<p>On executing the above code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>The --help option</h3>

<p>This option prints the help message on standard output.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>The --lint[=fatal] option</h3>

<p>This option enables checking of non-portable or dubious constructs. When an argument <b>fatal</b> is provided, it treats warning messages as errors. The following example demonstrates this &minus;</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>The --posix option</h3>

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

<h3>The --profile[=file] option</h3>

<p>This option generates a pretty-printed version of the program in file. Default file is <b>awkprof.out</b>. Below simple example illustrates this &minus;</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>The --traditional option</h3>

<p>This option disables all gawk-specific extensions.</p>

<h3>The --version option</h3>

<p>This option displays the version information of the AWK program.</p>

<p><b>Example</b></p>

<p>When this code is executed, it produces the following result &minus;</p>

<p><b>Output</b></p>

<p>&copy; Copyright 2017. All Rights Reserved.</p>

<pre class="result notranslate">

awk [options] file ...

<h3>Example</h3>

<p>Consider a text file <b>marks.txt</b> with the following content &minus;</p>

<pre class="result notranslate">

1) Amit Physics 80

2) Rahul Maths 90

3) Shyam Biology 87

4) Kedar English 85

5) Hari History 89

<p>Let us display the complete content of the file using AWK as follows &minus;</p>

<p><b>Example</b></p>

<pre class="prettyprint notranslate">

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

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<pre class="result notranslate">

1) Amit Physics 80

2) Rahul Maths 90

3) Shyam Biology 87

4) Kedar English 85

5) Hari History 89

<h2>AWK Program File</h2>

<p>We can provide AWK commands in a script file as shown &minus;</p>

<pre class="result notranslate">

awk [options] -f file ....

<p>First, create a text file <b>command.awk</b> containing the AWK command as shown below &minus;</p>

<pre class="result notranslate">

{print}

<p>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.</p>

<p><b>Example</b></p>

<pre class="prettyprint notranslate">

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

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<pre class="result notranslate">

1) Amit Physics 80

2) Rahul Maths 90

3) Shyam Biology 87

4) Kedar English 85

5) Hari History 89

<h2>AWK Standard Options</h2>

<p>AWK supports the following standard options which can be provided from the command line.</p>

<h3>The -v option</h3>

<p>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.</p>

<p><b>Example</b></p>

<pre class="prettyprint notranslate">

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

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<pre class="result notranslate">

Name = Jerry

<h3>The --dump-variables[=file] option</h3>

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

<p><b>Example</b></p>

<pre class="prettyprint notranslate">

[jerry]$ awk --dump-variables ''

[jerry]$ cat awkvars.out

<p>On executing the above code, you get the following result &minus;</p>

<p><b>Output</b></p>

<pre class="result notranslate">

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"

<h3>The --help option</h3>

<p>This option prints the help message on standard output.</p>

<p><b>Example</b></p>

<pre class="prettyprint notranslate">

[jerry]$ awk --help

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<pre class="result notranslate">

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

<h3>The --lint[=fatal] option</h3>

<p>This option enables checking of non-portable or dubious constructs. When an argument <b>fatal</b> is provided, it treats warning messages as errors. The following example demonstrates this &minus;</p>

<p><b>Example</b></p>

<pre class="prettyprint notranslate">

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

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<pre class="result notranslate">

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!

<h3>The --posix option</h3>

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

<h3>The --profile[=file] option</h3>

<p>This option generates a pretty-printed version of the program in file. Default file is <b>awkprof.out</b>. Below simple example illustrates this &minus;</p>

<p><b>Example</b></p>

<pre class="prettyprint notranslate">

[jerry]$ awk --profile 'BEGIN{printf"---|Header|--\n"} {print}

END{printf"---|Footer|---\n"}' marks.txt &gt; /dev/null

[jerry]$ cat awkprof.out

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<pre class="result notranslate">

# 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"

}

<h3>The --traditional option</h3>

<p>This option disables all gawk-specific extensions.</p>

<h3>The --version option</h3>

<p>This option displays the version information of the AWK program.</p>

<p><b>Example</b></p>

<pre class="prettyprint notranslate">

[jerry]$ awk --version

<p>When this code is executed, it produces the following result &minus;</p>

<p><b>Output</b></p>

<pre class="result notranslate">

GNU Awk 4.0.1

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

<title>AWK Basic Examples</title>

<h1>AWK - Basic Examples</h1>

<p>This chapter describes several useful AWK commands and their appropriate examples. Consider a text file <b>marks.txt</b> to be processed with the following content &minus;</p>

<h2>Printing Column or Field</h2>

<p>You can instruct AWK to print only certain columns from the input field. The following example demonstrates this &minus;</p>

<h3>Example</h3>

<p>On executing this code, you get the following result &minus;</p>

<h3>Output</h3>

<p>In the file <b>marks.txt</b>, the third column contains the subject name and the fourth column contains the marks obtained in a particular subject. Let us print these two columns using AWK print command. In the above example, <b>$3 and $4</b> represent the third and the fourth fields respectively from the input record.</p>

<h2>Printing All Lines</h2>

<p>By default, AWK prints all the lines that match pattern.</p>

<h3>Example</h3>

<p>On executing this code, you get the following result &minus;</p>

<h3>Output</h3>

<p>In the above example, we are searching form pattern <b>a</b>. When a pattern match succeeds, it executes a command from the body block. In the absence of a body block &minus; default action is taken which is print the record. Hence, the following command produces the same result &minus;</p>

<h3>Example</h3>

<h2>Printing Columns by Pattern</h2>

<p>When a pattern match succeeds, AWK prints the entire record by default. But you can instruct AWK to print only certain fields. For instance, the following example prints the third and fourth field when a pattern match succeeds.</p>

<h3>Example</h3>

<p>On executing this code, you get the following result &minus;</p>

<h3>Output</h3>

<h2>Printing Column in Any Order</h2>

<p>You can print columns in any order. For instance, the following example prints the fourth column followed by the third column.</p>

<h3>Example</h3>

<p>On executing the above code, you get the following result &minus;</p>

<h3>Output</h3>

<h2>Counting and Printing Matched Pattern</h2>

<p>Let us see an example where you can count and print the number of lines for which a pattern match succeeded.</p>

<h3>Example</h3>

<p>On executing this code, you get the following result &minus;</p>

<h3>Output</h3>

<p>In this example, we increment the value of counter when a pattern match succeeds and we print this value in the END block. Note that unlike other programming languages, there is no need to declare a variable before using it.</p>

<h2>Printing Lines with More than 18 Characters</h2>

<p>Let us print only those lines that contain more than 18 characters.</p>

<h3>Example</h3>

<p>On executing this code, you get the following result &minus;</p>

<h3>Output</h3>

<p>AWK provides a built-in <b>length</b> function that returns the length of the string. <b>$0</b> variable stores the entire line and in the absence of a body block, default action is taken, i.e., the print action. Hence, if a line has more than 18 characters, then the comparison results true and the line gets printed.</p>

<p>&copy; Copyright 2017. All Rights Reserved.</p>

<pre class="result notranslate">

1) Amit Physics 80

2) Rahul Maths 90

3) Shyam Biology 87

4) Kedar English 85

5) Hari History 89

<h2>Printing Column or Field</h2>

<p>You can instruct AWK to print only certain columns from the input field. The following example demonstrates this &minus;</p>

<h3>Example</h3>

<pre class="prettyprint notranslate">

[jerry]$ awk '{print $3 "\t" $4}' marks.txt

<p>On executing this code, you get the following result &minus;</p>

<h3>Output</h3>

<pre class="result notranslate">

Physics 80

Maths 90

Biology 87

English 85

History 89

<p>In the file <b>marks.txt</b>, the third column contains the subject name and the fourth column contains the marks obtained in a particular subject. Let us print these two columns using AWK print command. In the above example, <b>$3 and $4</b> represent the third and the fourth fields respectively from the input record.</p>

<h2>Printing All Lines</h2>

<p>By default, AWK prints all the lines that match pattern.</p>

<h3>Example</h3>

<pre class="prettyprint notranslate">

[jerry]$ awk '/a/ {print $0}' marks.txt

<p>On executing this code, you get the following result &minus;</p>

<h3>Output</h3>

<pre class="result notranslate">

2) Rahul Maths 90

3) Shyam Biology 87

4) Kedar English 85

5) Hari History 89

<p>In the above example, we are searching form pattern <b>a</b>. When a pattern match succeeds, it executes a command from the body block. In the absence of a body block &minus; default action is taken which is print the record. Hence, the following command produces the same result &minus;</p>

<h3>Example</h3>

<pre class="prettyprint notranslate">

[jerry]$ awk '/a/' marks.txt

<h2>Printing Columns by Pattern</h2>

<p>When a pattern match succeeds, AWK prints the entire record by default. But you can instruct AWK to print only certain fields. For instance, the following example prints the third and fourth field when a pattern match succeeds.</p>

<h3>Example</h3>

<pre class="prettyprint notranslate">

[jerry]$ awk '/a/ {print $3 "\t" $4}' marks.txt

<p>On executing this code, you get the following result &minus;</p>

<h3>Output</h3>

<pre class="result notranslate">

Maths 90

Biology 87

English 85

History 89

<h2>Printing Column in Any Order</h2>

<p>You can print columns in any order. For instance, the following example prints the fourth column followed by the third column.</p>

<h3>Example</h3>

<pre class="prettyprint notranslate">

[jerry]$ awk '/a/ {print $4 "\t" $3}' marks.txt

<p>On executing the above code, you get the following result &minus;</p>

<h3>Output</h3>

<pre class="result notranslate">

90 Maths

87 Biology

85 English

89 History

<h2>Counting and Printing Matched Pattern</h2>

<p>Let us see an example where you can count and print the number of lines for which a pattern match succeeded.</p>

<h3>Example</h3>

<pre class="prettyprint notranslate">

[jerry]$ awk '/a/{++cnt} END {print "Count = ", cnt}' marks.txt

<p>On executing this code, you get the following result &minus;</p>

<h3>Output</h3>

<pre class="result notranslate">

Count = 4

<p>In this example, we increment the value of counter when a pattern match succeeds and we print this value in the END block. Note that unlike other programming languages, there is no need to declare a variable before using it.</p>

<h2>Printing Lines with More than 18 Characters</h2>

<p>Let us print only those lines that contain more than 18 characters.</p>

<h3>Example</h3>

<pre class="prettyprint notranslate">

[jerry]$ awk 'length($0) &gt; 18' marks.txt

<p>On executing this code, you get the following result &minus;</p>

<h3>Output</h3>

<pre class="result notranslate">

3) Shyam Biology 87

4) Kedar English 85

<title>AWK Built-in Variables</title>

<h1>AWK - Built-in Variables</h1>

<p>AWK provides several built-in variables. They play an important role while writing AWK scripts. This chapter demonstrates the usage of built-in variables.</p>

<h2>Standard AWK variables</h2>

<p>The standard AWK variables are discussed below.</p>

<h3>ARGC</h3>

<p>It implies the number of arguments provided at the command line.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<p>But why AWK shows 5 when you passed only 4 arguments? Just check the following example to clear your doubt.</p>

<h3>ARGV</h3>

<p>It is an array that stores the command-line arguments. The array's valid index ranges from 0 to ARGC-1.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>CONVFMT</h3>

<p>It represents the conversion format for numbers. Its default value is <b>%.6g</b>.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>ENVIRON</h3>

<p>It is an associative array of environment variables.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<p>To find names of other environment variables, use <b>env</b> command.</p>

<h3>FILENAME</h3>

<p>It represents the current file name.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<p>Please note that FILENAME is undefined in the BEGIN block.</p>

<h3>FS</h3>

<p>It represents the (input) field separator and its default value is space. You can also change this by using <b>-F</b> command line option.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>NF</h3>

<p>It represents the number of fields in the current record. For instance, the following example prints only those lines that contain more than two fields.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>NR</h3>

<p>It represents the number of the current record. For instance, the following example prints the record if the current record contains less than three fields.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>FNR</h3>

<p>It is similar to NR, but relative to the current file. It is useful when AWK is operating on multiple files. Value of FNR resets with new file.</p>

<h3>OFMT</h3>

<p>It represents the output format number and its default value is <b>%.6g</b>.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>OFS</h3>

<p>It represents the output field separator and its default value is space.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>ORS</h3>

<p>It represents the output record separator and its default value is newline.</p>

<p><b>Example</b></p>

<p>On executing the above code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>RLENGTH</h3>

<p>It represents the length of the string matched by <b>match</b> function. AWK's match function searches for a given string in the input-string.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>RS</h3>

<p>It represents (input) record separator and its default value is newline.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>RSTART</h3>

<p>It represents the first position in the string matched by <b>match</b> function.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>SUBSEP</h3>

<p>It represents the separator character for array subscripts and its default value is <b>\034</b>.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>$0</h3>

<p>It represents the entire input record.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>$n</h3>

<p>It represents the n^th field in the current record where the fields are separated by FS.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h2>GNU AWK Specific Variables</h2>

<p>GNU AWK specific variables are as follows &minus;</p>

<h3>ARGIND</h3>

<p>It represents the index in ARGV of the current file being processed.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>BINMODE</h3>

<p>It is used to specify binary mode for all file I/O on non-POSIX systems. Numeric values of 1, 2, or 3 specify that input files, output files, or all files, respectively, should use binary I/O. String values of <b>r</b> or <b>w</b> specify that input files or output files, respectively, should use binary I/O. String values of <b>rw</b> or <b>wr</b> specify that all files should use binary I/O.</p>

<h3>ERRNO</h3>

<p>A string indicates an error when a redirection fails for <b>getline</b> or if <b>close</b> call fails.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>FIELDWIDTHS</h3>

<p>A space separated list of field widths variable is set, GAWK parses the input into fields of fixed width, instead of using the value of the FS variable as the field separator.</p>

<h3>IGNORECASE</h3>

<p>When this variable is set, GAWK becomes case-insensitive. The following example demonstrates this &minus;</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>LINT</h3>

<p>It provides dynamic control of the <b>--lint</b> option from the GAWK program. When this variable is set, GAWK prints lint warnings. When assigned the string value fatal, lint warnings become fatal errors, exactly like <b>--lint=fatal</b>.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>PROCINFO</h3>

<p>This is an associative array containing information about the process, such as real and effective UID numbers, process ID number, and so on.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<h3>TEXTDOMAIN</h3>

<p>It represents the text domain of the AWK program. It is used to find the localized translations for the program's strings.</p>

<p><b>Example</b></p>

<p>On executing this code, you get the following result &minus;</p>

<p><b>Output</b></p>

<p>The above output shows English text due to <b>en_IN</b> locale</p>

<p>&copy; Copyright 2017. All Rights Reserved.</p>

<pre class="prettyprint notranslate">

[jerry]$ awk 'BEGIN {print "Arguments =", ARGC}' One Two Three Four