How to grep out substring which can change?

Question

Basically I have a very large text file and each line contains

tag=yyyyy;id=xxxxx;db_ref=zzzzz; 

What I want is to grep out the id, but the id

Answer 1

Try the following:

grep -oP 'id=\K[^;]*' file

Answer 2

Via grep:

grep -o 'id=[^;]*'

Via awk:

awk -F';' '{ print $2}' testlog
id=xxxxx

edit: see sudo_O's answer for the look-behind. it's more to the point of your question, IMO.

Answer 3

You could try this awk. It should also work if there are multiple id= entries per line and it would not give a false positive for ...;pid=blabla;...

awk '/^id=/' RS=\; file

Answer 4

try :

grep -Po "(?<=id=)[^;]*" file

Answer 5

You could do:

$ grep -o 'id=[^;]*' file

And if you don't want to inlcude the id= part you can using positive look-behind:

$ grep -Po '(?<=id=)[^;]*' file

Answer 6

perl -lne 'print $1 if(/id=([^\;]*);/)' your_file

tested:

> echo "tag=yyyyy;id=xxxxx;db_ref=zzzzz; "|perl -lne 'print $1 if(/id=([^\;]*);/)'
xxxxx
>