topic Re: Help with grep and if in Operating System - Linux

Help with grep and if

dictum9 — Thu, 15 Feb 2007 10:52:07 GMT

I need code like this:

if [[ grep string $file ]]
then
file contains string
else
file does not contain string

fi

I got this but it errors on "]]"

Re: Help with grep and if

Wouter Jagers — Thu, 15 Feb 2007 10:59:21 GMT

hi,

if [ `grep string $file | wc -l` -gt 0 ]
..

should work better.

Cheers

Re: Help with grep and if

gstonian — Thu, 15 Feb 2007 11:02:34 GMT

try

FOUND=`grep string $file`
if [[ -n $FOUND ]]
then
contains value
else
contains nothing

-n is non zero check whereas -z is a zero check

Cheers

Re: Help with grep and if

Peter Godron — Thu, 15 Feb 2007 11:06:23 GMT

Hi,

a=`grep 09 $file`
if [ -n "$a" ]
then
echo file contains string
else
echo file does not contain string
fi

Re: Help with grep and if

Heironimus — Thu, 15 Feb 2007 11:21:06 GMT

If you don't actually need to keep the matching lines you can use grep's exit code.

if grep 'string' "$file" 1>/dev/null 2>&1 ; then
echo "$file contains string"
else
echo "$file doesn't contain string, please add some"
fi

Re: Help with grep and if

dictum9 — Thu, 15 Feb 2007 11:22:03 GMT

I actually got it to work by removing the [[ and ]]

Re: Help with grep and if

James R. Ferguson — Thu, 15 Feb 2007 11:34:26 GMT

Hi:

The 'grep' filter will return zero (0) if there are matches; one (1) if not. Hence:

# grep local /etc/hosts > /dev/null || echo "no matches!"

...is a terse way to meet your goal.

You can also count and return the number of matches with the '-c' switch. See the manpages for more information.

Regards!

...JRF...

Re: Help with grep and if

Dennis Handly — Thu, 15 Feb 2007 12:17:06 GMT

You can improve Heironimus' solution by using grep -q, to not produce any output.

Re: Help with grep and if

Sandman! — Thu, 15 Feb 2007 12:24:09 GMT

Unless there is a compelling reason to use the if statement, you could always use the following:

# grep string file && echo file contains string || echo file does not contain string

~cheers

Re: Help with grep and if

Daavid Turnbull — Thu, 15 Feb 2007 20:47:40 GMT

I always just use the exit code from grep:

grep -q string $file
if [ $? -eq 0 ]
then
echo "string is in $file"
else
echo "string is not in $file"
fi

Your friends here are:

man test
man grep

Re: Help with grep and if

Bill Hassell — Thu, 15 Feb 2007 22:46:12 GMT

And another solution: grep -c which counts the matches:

[ $(grep -c $STRING $FILE) = 0 ] \
&& echo no match || echo match