Differences

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

--- linux_wiki:awk [2015/08/13 22:30]
billdozor
+++ linux_wiki:awk [2019/05/25 23:50] (current)
@@ Line 6: / Line 6: @@
 Gawk is the GNU Project's implementation of the AWK programming language.
-I typically stick to using gawk and in most cases, awk is a symlink to gawk.
+In most cases, awk is a symlink to gawk.
-This page will contain useful gawk commands as I run into them.
 **Checklist**
-  * Distros: All
+  * Distro(s): Any
-  * gawk installed
+  * 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
 ----
@@ Line 38: / Line 48: @@
 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.
+----