Check if process is running

Question

I am trying to check if a process is running. If it is running I want a return value of 'OK' and if not a return value of 'Not OK'. I can only use 'ps' without any other arguments attached (eg. ps -ef) if thats the correct term. The code I have is:

if ps | grep file; then  echo 'OK'; else  echo 'NO'; fi

The problem with this is that it does not search for the exact process and always returns 'OK', I don't want all the information to appear I just want to know if the file exists or not.

Solution 1

Your code always returns 'OK', because grep finds itself in the process list ('grep file' contains the word 'file'). A fix would be to do a `grep -e [f]ile' (-e for regular expression), which doesn't find itself.

Solution 2

Spare grep for real problems:

ps -C file

avoids the problem of using grep altogether.

Solution 3

ps | grep -q '[f]ile'

Solution 4

When I know the pid I prefer:

[ -d /proc/<pid> ] && echo OK || echo NO

Solution 5

What about "pgrep"?

$ pgrep -x foo
xxxx
$

where xxxx is the pid of the binary running with the name foo. If foo is not running, then no output.

Also:

$ if [[ pgrep -x foo ]]; then echo "yes"; else echo "no" ; fi;

will print "yes" if foo is running; "no" if not.

see pgrep man page.

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