note naikonta OK, here is the expanded version of the original OP's oneliner, following [tye]'s [id://674716|explanation]: <code> cat fatals.pl #!/usr/bin/perl use strict; use warnings FATAL => 'all'; my $cmd = shift || '_bad_exe_ a b c'; print "I'm parent with id $$\n"; eval { my $pid = open CMD, "-|"; if ($pid) { print "I'm forking a child with id $pid\n"; print while <CMD>; } else { #no warnings; # get rid of warnings on "Can't exec:..." print "[$$] I'm child, about to exec [$cmd]\n"; exec $cmd; } }; die "[$$] ERROR: $@" if $@; print "[$$]HOW DID I GET HERE?\n"; </code> Run with correct command (just as comparisson): <code> $ perl fatals.pl ls I'm parent with id 6238 I'm forking a child with id 6239 [6239] I'm child, about to exec [ls] 642663.pl 642676.pl 642682.pl 644761.pl </code> No problem there. Now, run with no args (default command): <code> $ perl fatals.pl I'm parent with id 6240 [6241] ERROR: Can't exec "_bad_exe_": No such file or directory at fatals.pl line 18. I'm forking a child with id 6241 [6241] I'm child, about to exec [_bad_exe_ a b c] [6240]HOW DID I GET HERE? </code> So I guess, it's the child that triggers the "Can't exec ..." warning that gets "upgraded" into fatal error (due to FATAL), trapped in $@, and dies. The child dies, the parent doesn't, that's <i>HOW DID I GET HERE</i>, I suppose. OTOH, if the <c>no warnings;</c> is uncommented, then well, no "Can't exec..." warning, no $@ trapping, and the child lives pretending nothing happens, yet covering up by asking <i>HOW DID I GET HERE</i>. <div class="pmsig"><div class="pmsig-607636"> <hr size="1" noshade="1"> <p align="right"><small> <i>Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!</i></small></p> </div></div> 674657 674657