grep a file, but show several surrounding lines?

Question

I would like to grep for a string, but show the preceding 5 lines and following 5 lines as well as the matched line. I'm scanning for errors in a logfile, and want to see the context.

Any clues for the clueless?

Answer 1

For GNU grep you can use -B num to set how many lines before the match and -A num for the number of lines after the match.

grep -B 3 -A 2 foo README.txt

If you want the same amount of lines before and after you can use -C num.

grep -C 3 foo README.txt

This will show 3 lines before and 3 lines after.

Answer 2

grep astring myfile -A 5 -B 5

That will grep "myfile" for "astring", and show 5 lines before and after each match

Answer 3

-A and -B will work, as will -C n (for n lines of context), or just -n (for n lines of context).

Answer 4

I've used -A and -B before, but just now learned about -C n and -n. Thanks Stu.

Answer 5

I normally use

grep searchstring file -C n # n for number of lines of context up and down

Many of the tools like grep also have really great man files too. I find myself referring to grep's man page a lot because there is so much you can do with it.

man grep

Many GNU tools also have an info page that may have more useful information in addition to the man page.

info grep

Answer 6

I keep a copy of Brendan Gregg's perl script around for this purpose. Works well.

Answer 7

Ack works with similar arguments than grep, and accept -C. But it's usually better for searching through code.