Question

I was wondering if it was possible to manually wake a perl script that has gone to sleep.
Basically I set my script to sleep for say an hour after performing something, and 10 minutes later I realize I want it to run again.

The platform I’m running on is linux, with a tcsh shell.

Again, Thanks for any help

Answer 1

On many systems, system calls like sleep can be interrupted with signals. On such an interruption, sleep will return the number of seconds that it actually slept for and set $!. Of course you have to use a signal that will allow your script to continue. If you haven’t set any specific signal handler, a combination of SIGSTOP and SIGCONT will do the trick, too.

Example:

$ perl -e 'print "slept for ", sleep 1000, " seconds.\n";' &
[2] 6220
$ kill -STOP 6220
$ kill -CONT 6220
slept for 8 seconds[2]+  Stopped     perl -e ...

Another example (trivial SIGUSR1 handler):

$ perl -e '$SIG{USR1}=sub{}; print "slept for ", sleep 1000, "s.\n"' &
[1] 2419
$ kill -USR1 2419
slept for 4s