[SOLVED] Grep until certain character or pattern appears

ohijames · 06-25-2010, 01:43 PM

Hi,

I have the following command that greps "/etc/cron.allow" and displays the following 9 lines of $file
grep -A 9 "/etc/cron.allow" $file

On the other hand I would like to grep a file for a certain text display the next couple of lines and stop when i hit a specified word or blank or pattern.

Basically I would like my grep to end when the shell hits a blank, certain key word or pattern specified in command.

Thanks.

rweaver · 06-25-2010, 01:55 PM

add another grep:

Code:

grep -A9 "/etc/cron.allow" $file | grep -B9 "pattern"

so what happens is...

Code:

core:~$ grep -A9 "/etc/cron.allow" test.txt
cron.allow
asdf
asdf

asdf
dfda
asdf
asdf
aasdfffds
core:~$ grep -A9 "/etc/cron.allow" test.txt | grep -B9 "^$"
cron.allow
asdf
asdf

core:~$

Since grep only passes the data you specified to the pipe and it can't pass more lines than that, the second grep limits it back to beginning of whatever matched at most from the point it occurs.

Might be more applicable to output the grep and clean it up though if your input is complex.

Robhogg · 06-25-2010, 03:23 PM

An alternative way to do this could be using sed:

Code:

sed -n '/cron.allow/,/\<word\>\|^$\|pattern/p' $file

The -n switch turns off sed's normal behaviour (to print every line of $file), while the command in single quotes tells it to print everything between line(s) containing 'cron.allow' and the next line either containing ' word ', or matching 'pattern', or being blank (^$).

rweaver · 06-25-2010, 04:09 PM

Quote:

Originally Posted by Robhogg

An alternative way to do this could be using sed:

Code:

sed -n '/cron.allow/,/\<word\>\|^$\|pattern/p' $file

I agree with Rob's use of sed here (or awk as an alternative), sed is better suited to this particular application than grep. An added advantage if you learn a little sed you don't ever need grep and sed is considerably more powerful (awk even more so than sed, although the syntax is typically a bit more complex for 'easy things')