Bash – Listen for exit of process given pid $$

bashprocprocessshell-script

Say I have a pid in hand, mypid=$$

is there some bash/system command I can use to listen for the exit of that process with the given pid?

If no process with mypid exists, I guess the command should simply fail.

Best Answer

I got what I needed from this answer: https://stackoverflow.com/a/41613532/1223975

..turns out using wait <pid> will only work if that pid is a child process of the current process.

However the following will work for any process:

To wait for any process to finish

Linux:

tail --pid=$pid -f /dev/null

Darwin (requires that $pid has open files):

lsof -p $pid +r 1 &>/dev/null

With timeout (seconds)

Linux:

timeout $timeout tail --pid=$pid -f /dev/null

Darwin (requires that $pid has open files):

lsof -p $pid +r 1m%s -t | grep -qm1 $(date -v+${timeout}S +%s 2>/dev/null || echo INF)

Related Solutions

Shell – bash – get pid for a script using the script filename

Try pgrep -f running_script -- the -f option uses the whole command line to match against, not just the process name

Process Management – How to Check if a Given PID is Running

The perl function kill(0,$pid) can be used.

If the return code is 1 then the PID exists and you're allowed to send a signal to it.

If the return code is 0 then you need to check $!. It may be EPERM (permission denied) which means the process exists or ESRCH in which case the process doesn't exist.

If your checking code is running as root then you can simplify this to just checking the return code of kill; 0=>error, 1=>ok

For example:

% perl -d -e 0

Loading DB routines from perl5db.pl version 1.37
Editor support available.

Enter h or 'h h' for help, or 'man perldebug' for more help.

main::(-e:1):   0
  DB<1> print kill(0,500)
0
  DB<2> print $!
No such process
  DB<3> print kill(0,1)
0
  DB<4> print $!
Operation not permitted
  DB<5> print kill(0,$$)
1

This can be made into a simple function

use Errno;

sub test_pid($)
{
  my ($pid)=@_;

  my $not_present=(!kill(0,$pid) && $! == Errno::ESRCH);

  return($not_present);
}

print "PID 500 not present\n" if test_pid(500);
print "PID 1 not present\n" if test_pid(1);
print "PID $$ not present\n" if test_pid($$);