How can I make Perl wait for child processes started in the background with system()?

Question

I have some Perl code that executes a shell script for multiple parameters, to simplify, I\'ll just assume that I have code that looks like this:

for $p (@a){
           


        

Answer 1

You are going to have to change something, changing the code to use fork is probably simpler, but if you are dead set against using fork, you could use a wrapper shell script that touches a file when it is done and then have your Perl code check for the existence of the files.

Here is the wrapper:

#!/bin/bash

$*

touch /tmp/$2.$PPID

Your Perl code would look like:

for my $p (@a){
    system("/path/to/wrapper.sh /path/to/file.sh $p &");
}
while (@a) {
    delete $a[0] if -f "/tmp/$a[0].$$";
}

But I think the forking code is safer and clearer:

my @pids;
for my $p (@a) {
    die "could not fork" unless defined(my $pid = fork);\
    unless ($pid) { #child execs
        exec "/path/to/file.sh", $p;
        die "exec of file.sh failed";
    }
    push @pids, $pid; #parent stores children's pids
}

#wait for all children to finish
for my $pid (@pids) {
    waitpid $pid, 0;
}