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

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