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This shows you the differences between two versions of the page.

--- linux_wiki:awk [2016/05/30 17:09]
billdozor [Print Line After Match]
+++ linux_wiki:awk [2019/05/25 23:50]
@@ Line 1: / Line 1: @@
-====== 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
-----
-====== 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 - $number => The fields
-  * NF => Number of fields on the current line
-  * NR => Current line number
-----
-===== Gsub =====
-gawk's gsub string function matches and replaces regular expressions. This can replace a grep | sed combination.
-<code bash>
-~$ 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)
-----
-===== 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>
-----
-===== 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
-----
-===== 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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