topic Re: Grep issue in Operating System - Linux

Grep issue

Mark Misselbrook — Thu, 20 Jan 2005 10:23:48 GMT

I need to grep a string from an output file, but when I get a match I also need the line above and below the matching line i.e

lines read as follows:

----10.70.110.18 PING Statistics----
2 packets transmitted, 1 packets received, 50% packet loss
Mon Jan 17 12:45:49 GMT 2005

HELP!!!!!!!!!!!!!!!!

Re: Grep issue

John Poff — Thu, 20 Jan 2005 10:40:37 GMT

Hi,

If you are on Linux and using the GNU grep, you can use the -B 1 option to print the line before the matching line, and the -C 1 option to print the line after.

JP

Re: Grep issue

Francisco J. Soler — Thu, 20 Jan 2005 10:44:05 GMT

Hi Mark, you can do it with awk like this:

awk '/expresion/ {print prev ; print $0 ; getline ; print $0}
{prev=$0}' file_in

If you want, you can create a file like this:
----- file.awk -----
/expresion/ {print prev ; print $0 ; getline ; print $0}
{prev=$0}
-------- end file.awk -----------

Then you can type:

awk -f file.awk file_in

and get the same result.

Frank.

Re: Grep issue

Sergejs Svitnevs — Thu, 20 Jan 2005 12:36:15 GMT

Mark,

Here is the solution:

cat | sed -n -e '//{x;1!p;g;$!N;p;D;}' -e h

Regards,
Sergejs

Re: Grep issue

Dave Falloon — Thu, 20 Jan 2005 19:53:09 GMT

John was close, the -C 1 gives both the line immediately before and after the matched line.

Here's right out of the gnu grep man page:

OPTIONS
-A NUM, --after-context=NUM Print NUM lines of trailing context after matching lines. Places a line containing -- between contiguous groups of matches.
-B NUM, --before-context=NUM Print NUM lines of leading context before matching lines. Places a line containing -- between contiguous groups of matches.
-C NUM, --context=NUM Print NUM lines of output context. Places a line containing -- between contiguous groups of matches.

hope that helps,

--Dave

Re: Grep issue

Mark Misselbrook — Fri, 21 Jan 2005 05:24:19 GMT

The sed solution from Sergejs worked perfectly.

10 points