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

• -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

gawk's gsub string function matches and replaces regular expressions. This can replace a grep | sed combination.

~$ echo -e "Hello, friend.\nHello, how are you?\nI am fine." | gawk 'gsub(/Hello/,"Goodbye")'
Goodbye, friend.
Goodbye, how are you?

Notice that the last line “I am fine.” is not displayed at all because it doesn't match the regex. (Hello)

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

VERSION=4.3.0
echo | gawk -v n1=${VERSION} -v n2=3.5.3  '{if (n1>=n2) print ("true"); else print ("false");}'
 
true

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

awk '/mystring/ { getline; print }'

• mystring ⇒ regex string to search for
• getline ⇒ set the line $0 to the next line
• print ⇒ print the line

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.

1. Find users and account disabled status

   /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

2. Narrow it down to just usernames and True/False values

   /usr/bin/ipa user-find --sizelimit=0 --all | grep -E "(User login|Account disabled)" | awk '{print $3}'
    
   rjones
   False
   sanderson
   True

3. Add in the awk magic that will display ONLY the username with “False” after it (Not Disabled)

   /usr/bin/ipa user-find --sizelimit=0 --all | grep -E "(User login|Account disabled)" | awk '{print $3}' | awk '/False/ { print x }; { x=$0 }'
    
   rjones

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.