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How to use awk command (string extraction)

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This section explains how to use the awk command for string extraction, which can be used to extract the desired information from the results of a command output in tabular form.

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Format

awk [options] [command] [file...]

Examples of Use

Display specified field
( '{print $1, $3}' )

Only specific fields are displayed among the fields separated by spaces.

$ cat test.txt 
1111 aaaa AAAA
2222 bbbb BBBB
3333 cccc CCCC
$ awk '{print $1, $3}' test.txt 
1111 AAAA
2222 BBBB
3333 CCCC

Change delimiter ( -F )

The -F option can be used to specify a delimiter.

$ cat test.txt 
1111,aaaa,AAAA
2222,bbbb,BBBB
3333,cccc,CCCC
$ awk -F',' '{print $1, $3}' test.txt 
1111 AAAA
2222 BBBB
3333 CCCC

Let’s specify two delimiters, : and /.

$ echo "111:aaa/bbb" | awk -F'[:/]' '{print $1, $3}'
111 bbb

Specify pattern

If you write 'pattern {action}', the action will be performed only on rows matching the pattern.

In the following example, only rows that match the conditions that the row number is greater than 1 and the fifth field is 256 are output.

$ ls -l
total 0
drwxr-xr-x  22 root  staff   704 Apr 12 23:38 Auth
drwxr-xr-x  14 root  staff   448 Apr 12 23:38 Broadcasting
drwxr-xr-x   6 root  staff   192 Apr 12 23:38 Bus
drwxr-xr-x  26 root  staff   832 Apr 12 23:38 Cache
drwxr-xr-x   4 root  staff   128 Apr 12 23:38 Config
drwxr-xr-x  12 root  staff   384 Apr 12 23:38 Console
drwxr-xr-x   7 root  staff   224 Apr 12 23:38 Container
drwxr-xr-x  31 root  staff   992 Apr 12 23:38 Contracts
drwxr-xr-x   6 root  staff   192 Apr 12 23:38 Cookie
drwxr-xr-x  29 root  staff   928 Apr 12 23:38 Database
drwxr-xr-x   5 root  staff   160 Apr 12 23:38 Encryption
drwxr-xr-x   6 root  staff   192 Apr 12 23:38 Events
drwxr-xr-x   8 root  staff   256 Apr 12 23:38 Filesystem
drwxr-xr-x  22 root  staff   704 Apr 12 23:38 Foundation
drwxr-xr-x   7 root  staff   224 Apr 12 23:38 Hashing
drwxr-xr-x  16 root  staff   512 Apr 12 23:38 Http
drwxr-xr-x   7 root  staff   224 Apr 12 23:38 Log
drwxr-xr-x  14 root  staff   448 Apr 12 23:38 Mail
drwxr-xr-x  20 root  staff   640 Apr 12 23:38 Notifications
drwxr-xr-x   9 root  staff   288 Apr 12 23:38 Pagination
drwxr-xr-x   6 root  staff   192 Apr 12 23:38 Pipeline
drwxr-xr-x  32 root  staff  1024 Apr 12 23:38 Queue
drwxr-xr-x   8 root  staff   256 Apr 12 23:38 Redis
drwxr-xr-x  36 root  staff  1152 Apr 12 23:38 Routing
drwxr-xr-x  16 root  staff   512 Apr 12 23:38 Session
drwxr-xr-x  27 root  staff   864 Apr 12 23:38 Support
drwxr-xr-x   8 root  staff   256 Apr 12 23:38 Translation
drwxr-xr-x  17 root  staff   544 Apr 12 23:38 Validation
drwxr-xr-x  13 root  staff   416 Apr 12 23:38 View
$
$ ls -l | awk 'NR>1 && $5==256 {print $5, $9}'
256 Filesystem
256 Redis
256 Translation

Extract specific rows to specific rows

Using awk, you can extract the contents from a line that contains a specific string to a line that contains a specific string.

<div>
  <h1>Hello World</h1>
  <ul class="list-main">
    <li>aaaaa</li>
    <li>bbbbb</li>
  </ul>
  <h3>Essential Links</h3>
  <ul class="list-sub">
    <li>11111</li>
    <li>22222</li>
    <li>33333</li>
  </ul>
</div>

To extract the lines from <ul class="list-main"> to </ul> in the above HTML, do the following

$ cat tmp.html | awk '/<ul class="list-main"/,/<\/ul/'
  <ul class="list-main">
    <li>aaaaa</li>
    <li>bbbbb</li>
  </ul>
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