About grep


 
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# 1  
About grep

Dear all
My boss recomended me to update my script code like this.

Code:
PIDFile=`cat pid`
PIDMemory=`ps -ef | grep $PIDFile | grep -v grep`
if [ $? = 0 ];
then 
   touch /apps/airserv/binaries/ESB/flag_lockfile
	else
	 echo "Check the application......Starting process has failed!!!!!!!!!!!!!!!!!"

but i really don't understand the last grep Where his use suggests two times, beside if we are filtering a process, why -v? this flag bring to me the other process that do not match!!!
Any idea???
# 2  
ps -ef gives you all the process were running including your current grep command. that's why you should use -v option for last grep Smilie
# 3  
When you do 'ps | grep string', there's good odds grep will also show up, since it will be a running process containing the string you're looking for. A common band-aid is to patch 'grep -v grep' on the end to chop it out, but this usually isn't the best answer.

If you're on a system with /proc/, for example, you can check if the folder for the process still exists to tell if it's still running.

On some systems, you can also just do ps $PID to tell if a process is still running without having to process ps' output at all.

That's also a useless use of cat.

Code:
# Better way to read the file without cat
read PID < pidfile

if [ -d /proc/$PID ]
then
        echo "Process is still running"
else
        echo "Process does not exist"
fi

This User Gave Thanks to Corona688 For This Post:
# 4  
Pamu, i'm agree with you on that
Code:
ps -ef

show all the process even the others user, but, i'm agree with this command line until the first grep,
i mean the first grep that i passed the parameters with the value of the process that i'm trying to run, for me it's good enough, it's just my understanding, i'm trying my best learn of what teach me.
So for what, the second use of the grep and like this?
Code:
| grep -v grep`

# 5  
just try and see the output.

Code:
ps -ef | grep app

more on

what is your first grepgrep app also has your process name so it will result that grep also.

hope it helps Smilie
# 6  
Quote:
Originally Posted by Newer
So for what, the second use of the grep and like this?
Code:
| grep -v grep`

We already told you... It removes lines containing 'grep'.

Watch this:

Code:
$ ps aux | grep processname
tyler    24149  0.0  0.0   2008   524 pts/1    S+   13:26   0:00 grep --colour=auto processname

$

When you do ps | grep, you get grep in the output, because it has your string in it! So the -v grep is to remove lines containing grep...
# 7  
Thanks you guys, now it's clearer for me, my problem was that i didn't know that the result of the grep pint at the end of the line the word "grep".
Ok, so everything it's fine now. Thanks again!!!!
 

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