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Re^2: exec sometimes changes pid

by doom (Deacon)
on Aug 03, 2009 at 00:34 UTC ( #785307=note: print w/replies, xml ) Need Help??

in reply to Re: exec sometimes changes pid
in thread exec sometimes changes pid

Some preliminary trials show you're probably right (though I still don't see what could be different on these two systems... maybe a different version of some IPC::* module?). In any case, I was experimenting with the list form of exec for other reasons, and I finally made it through the gotchas:

my @cmd = ('perl', '-e print "child: id after exec: $$\n"; print "child: sees processes...\n " , grep { m/perl/ } `ps ax` , "\n"; ', ); print "parent: pre-fork id $$\n"; if ( my $pid = fork ) { # this is parent code print "parent: post-fork id $$\n"; print "parent: return from fork is: $pid\n"; sleep 3; print "parent: still here, with id $$\n"; print "parent: sees processes...\n " , grep { m/perl/ } `ps ax` , "\n"; } else { # this is child code die "cannot fork: $!" unless defined $pid; print "child believes it is: $$\n"; exec {$cmd[0]} @cmd; }

The gotchas:

  • You use the command name first ("indirect object" syntax, ala printing to a file handle), *and* have the command name again inside the list. The second one is what appears in the process listing, the first is the program that's actually run.
  • From the shell, you typically do a perl -e 'some code', but if you're going around the shell, those single quotes on the string fed to "-e" just get in the way: @cmd = ('perl', q{-e some code }).

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