grep for string and test if successfully or not

B-Boy · 02-17-2009, 05:20 AM

Hi guys I am using grep in a bash script to look for a string and i would like to check if the string was found

so my script goes a little some thing like this !!!

Code:

grep bboy /var/log/messages
echo $?

so assumed that since the string bboy was not in /var/log/messages I would get the value higher than 0 but wether or not the string is in /var/log/messages I still get the valure 0

why?

jschiwal · 02-17-2009, 05:28 AM

You can use
grep bboy /var/log/messages && <do if found> || <do if not found>

The results from grep could also be used with an if statement.

Look at the manpage for grep to find what the return values are. 0 = found; 1 = not found; 2 = error. Posix states that an error returns a value greater than 1, so to be portable, you might want to use that as the test condition.

B-Boy · 02-17-2009, 05:33 AM

Quote:

Originally Posted by jschiwal

You can use
grep bboy /var/log/messages && <do if found> || <do if not found>

The results from grep could also be used with an if statement.

Look at the manpage for grep to find what the return values are. 0 = found; 1 = not found; 2 = error. Posix states that an error returns a value greater than 1, so to be portable, you might want to use that as the test condition.

thanks i dont know why i did not thing of that

jan61 · 02-17-2009, 01:43 PM

Moin,

a faster way is the -q option of the grep command - it stops parsing the file on first match (and you aren't flooded with the grep output because there is none):

Code:

grep -q bboy /var/log/messages && <do if found> || <do if not found>

Jan