I have a UNIX passwd file and i need to find using egrep if the first 7 characters from GECOS are inside the username. I want to check if the username (jkennedy) contains the word "kennedy" from the GECOS.
I was planning to use back-references but the username is before the gecos so i don't know how to implement it.
For example the passwd file contains this line:
jkennedy:x:2473:1067:kennedy john:/root:/bin/bash
As per my original comment, the regex below works for me.
See it in use here - note this regex differs slightly as it's more used for display purposes. The regex below is the POSIX version of this and removes non-capture groups and the unneeded capture group around the backreference.
^[^:]*([^:]{7})([^:]*:){4}\1.*$
^ assert position at the start of the line[^:]* match any character except : any number of times([^:]{7}) capture exactly seven of any character except :([^:]*:){4} match the following exactly four times
[^:]*: match any character except : any number of times, followed by : literally\1 match the backreference; matches what was previously matched by the first capture gorup.* match any character (except newline characters) any number of times$ assert position at the end of the line