grep question

yawe_frek · 01-05-2008, 03:04 AM

hi friends,

I seem to be having a little problem as to when to use this options of grep command

grep -A NUM
grep -B NUM

Kindly give me varoius life examples of how and when to use this options.

Thanks

angrybanana · 01-05-2008, 03:28 AM

Just to clarify what they do

Code:

$ cat file
first line
second line
third line

Code:

$ grep -A 1 second file
second line
third line

Code:

$ grep -B 1 second file
first line
second line

Here's a small example (not the best of examples but it works)

Code:

$ cat /var/lib/pacman/local/zip-2.32-1/desc
%NAME%
zip

%VERSION%
2.32-1

Code:

$ grep -A 1 %NAME% /var/lib/pacman/local/zip-2.32-1/desc|tail -1
zip

Of course awk does this better, but I can't think of any examples right now

pixellany · 01-05-2008, 06:09 AM

There are 3 options to print the context of a match: -A (after), -B (before), and -C(before and after)

In addition to the examples above, "grep -C5 <searchterm> <filename>" gives you 5 lines before and after the line with the match.

yawe_frek · 01-05-2008, 07:07 AM

Thanks so much for the quick reply, i really appreciate it. lets use the output of this command for both examples. Thanks

netstat -r|grep -A num