Make grep stop after first NON-matching line

Question

I'm trying to use grep to go through some logs and only select the most recent entries. The logs have years of heavy traffic on them so it's silly to do

    tac error.log | grep 2012
    tac error.log | grep "Jan.2012" 

etc.

and wait for 10 minutes while it goes through several million lines which I already know are not going to match. I know there is the -m option to stop at the first match but I don't know of a way to make it stop at first non-match. I could do something like grep -B MAX_INT -m 1 2011 but that's hardly an optimal solution.

Can grep handle this or would awk make more sense?

Answer 1

How about using awk like this:

tac error.log | awk '{if(/2012/)print;else exit}'

This should exit as soon as a line not matching 2012 is found.

Answer 2

Here is a solution in python:

# foo.py
import sys, re
for line in sys.stdin:
    if re.match(r'2012', line):
        print line,
        continue
    break

you@host> tac foo.txt | python foo.py