how to print 30 lines after regex

Poki · 06-09-2009, 03:28 PM

Hi all
Please help me find a way to print 30 lines after regex match

tx
Poki

jamescondron · 06-09-2009, 03:41 PM

What command are you currently using? And have you tried a man page? Or even asking your teacher?

H_TeXMeX_H · 06-10-2009, 10:20 AM

Please read man grep:

Code:

       -A NUM, --after-context=NUM
              Print NUM  lines  of  trailing  context  after  matching  lines.
              Places  a  line  containing  --  between  contiguous  groups  of
              matches.

pixellany · 06-10-2009, 11:58 AM

Homework??

Note that you never posted any follow-up in your other thread.

Poki · 06-11-2009, 09:42 AM

Thank you all for your valuable replies, i know very well how to use man pages, and no it is not a homework, i tried grep -A 30 it didn't work, that is the reason why i posted question

And regarding my previous post, none of the suggestions worked, so i didn't really need to thank anybody

colucix · 06-11-2009, 10:13 AM

No, you don't need to thank anybody if you don't want, but you need to explain the problem in details, since the grep -A option is the straightforward way to print N lines after a match and if it does not work for you, the problem must be addressed in a different way.

Questions:
- what exact command have you tried?
- what error message do you get?
- can you provide a real example?

Poki · 06-11-2009, 10:38 AM

You are probably right, i will redefine it:

i need to print n lines, between line number x and y, but x and y are variables so the easy way to do it with sed or awk don't work, because they accept numbers for line numbers and not variables.

sed -n '22531,22534p' /mylog

i need something like this:

sed -n '$fromLine,$toLinep' /mylog unfortunately this doesn't work

so my question is there a way to print n lines according to the range stored in variables.

Thank you
Poki

colucix · 06-11-2009, 10:43 AM

This issue is slightly different from the original one, since you're not trying to match a regexp anymore, right? The sed command fails because the single quotes prevent the shell variable substitution. You have to use double quotes or even no quotes at all. Also embed the name of the variable in brackets, otherwise $toLinep is treated as a variable name (included the p):

Code:

sed -n ${fromLine},${toLine}p /mylog

Poki · 06-11-2009, 10:57 AM

Quote:

Originally Posted by colucix

This issue is slightly different from the original one, since you're not trying to match a regexp anymore, right? The sed command fails because the single quotes prevent the shell variable substitution. You have to use double quotes or even no quotes at all. Also embed the name of the variable in brackets, otherwise $toLinep is treated as a variable name (included the p):

Code:

sed -n ${fromLine},${toLine}p /mylog

Thank you so much, it worked, i can finally print n lines according to variables, i googled so much for this answer.

First i thought i want to print n lines after i find regex, but then i reformulated it, because i found a way to find line numbers according to which i need to print log entries.