Shell Programming and Scripting

I want to do some operations provided the pid is active.

I assume you have the pid with you.

Code:

while kill -0 $pid
do
  echo "$pid is alive"
  # do your operations
done

In theory the only person who can reliably use a pid is the processes parent, as once a process dies, it's pid can get reused by another process. Then once wait/waitpid has returned that pid it is no longer valid.

In some systems pids range from 2 to 32767, if you had a webserver running one CGI program a second, then the pids would be reused every nine hours.

Hey...we can also check in one line command rite?
ps -ef | grep <pid> | grep -v grep

ps -p <PID>

If the process is alive then, this will return the process id with the time and command.

Not really, say of you were look for pid 241, it would return a false positive on all those 2410<=x<=2419 and 24100<=x<=24199 and other combinations.

This would only work if you owned the process.

Try...

Code:

if ps -p $id > /dev/null
then 
    : active
else
    : inactive
fi