ДОКУМЕНТАЦИЯТА!!!!: perldoc perlvar | less -p CHILD_ERROR

$ cat true.pl
#!/usr/bin/perl

print "TRUE\n";
print STDERR "TRUE\n";
exit(0);

$ cat false.pl
#!/usr/bin/perl

print "FALSE\n";
print STDERR "FALSE\n";
exit(3);

$ cat testexitcode.pl
#!/usr/bin/perl

open (T, " ./true.pl 2>&1 |") || die "no truth";
open (F, " ./false.pl 2>&1 |") || die "no lies";

while (<T>) { print; }; close(T);
print $? >> 8, "\n";

while (<F>) { print; }; close(F);
print $? >> 8, "\n";

$ perl testexitcode.pl
TRUE
TRUE
0
FALSE
FALSE
3

RTFM!
--sdg