====== Awk ======

**General Information**

AWK is a pattern scanning and processing language.
Gawk is the GNU Project's implementation of the AWK programming language.

In most cases, awk is a symlink to gawk.

**Checklist**
  * Distro(s): Any
  * Software: awk/gawk installed

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====== General Awk Variables ======

  * -F":" => Set the field seperator to colon (:), instead of spaces (default).
    * This can be set to any character
  * $0 => The entire line (excluding new line at the end)
  * $1 - $number => The fields
  * NF => Number of fields on the current line
  * NR => Current line number

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===== Gsub =====

gawk's gsub string function matches and replaces regular expressions. This can replace a grep | sed combination.
<code bash>
~$ echo -e "Hello, friend.\nHello, how are you?\nI am fine." | gawk 'gsub(/Hello/,"Goodbye")'
Goodbye, friend.
Goodbye, how are you?
</code>
Notice that the last line "I am fine." is not displayed at all because it doesn't match the regex. (Hello)

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===== Number Comparison =====

Bash doesn't have a really good way to compare floating point numbers. (Such as version numbers) This can be done very well with gawk.

Check to see if VERSION is >= to 3.5.3
<code bash>
VERSION=4.3.0
echo | gawk -v n1=${VERSION} -v n2=3.5.3  '{if (n1>=n2) print ("true"); else print ("false");}'

true
</code>

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===== Print Line After Match =====

Search for a regex string and print the line AFTER the match.

<code bash>
awk '/mystring/ { getline; print }'
</code>
  * mystring => regex string to search for
  * getline => set the line $0 to the next line
  * print => print the line

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===== Print Line Before Match =====

This trick allows you to search for a regex string, and print the line BEFORE the match.

FreeIPA Example: I want to get only enabled account usernames.

  - Find users and account disabled status<code bash>
/usr/bin/ipa user-find --sizelimit=0 --all | grep -E "(User login|Account disabled)"

User login: rjones
Account disabled: False
User login: sanderson
Account disabled: True
</code>
  - Narrow it down to just usernames and True/False values<code bash>
/usr/bin/ipa user-find --sizelimit=0 --all | grep -E "(User login|Account disabled)" | awk '{print $3}'

rjones
False
sanderson
True
</code>
  - Add in the awk magic that will display ONLY the username with "False" after it (Not Disabled)<code bash>
/usr/bin/ipa user-find --sizelimit=0 --all | grep -E "(User login|Account disabled)" | awk '{print $3}' | awk '/False/ { print x }; { x=$0 }'

rjones
</code>

**Explanation**
  * If the current line matches the regular expression "False" ("/False/"), then
    * Print the value of x ("{ print x }").
  * Next, store the current line in the variable "x" ("{ x=$0 }")  (Always do this; Does not matter if it matches)
    * This has the effect of making the previous line available when evaluating the next line.
      * Note: This will not work if the very first line matches the pattern, as x will not contain any lines yet.

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