Re: Boolean (was Boolian) operators defy my understanding...

system doesn't return true/false. Please refer to the documentation. For example, if the command was launched successfully and the exit code of the child process is 0, system returns 0.

my $rv = system(...);
if ($rv == -1) {
   die("Unable to launch child: $!\n");
}

if ($rv & 127) {
   die(sprintf("Error executing child: Child died with signal %d, %s c
+oredump\n",
      ($rv & 127),
      ($rv & 128) ? 'with' : 'without',
   ));
}

if ($rv >> 8) {
   die(sprintf("Error executing child: Child exited with value %d\n",
      ($rv >> 8)
   ));
}

print("Child ran successfully\n");
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Re^2: Boolean (was Boolian) operators defy my understanding... by cgmd (Beadle) on Jun 21, 2007 at 17:03 UTC
ikegami... I appreciate your comments and example code. I also have also found similar code (http://perldoc.perl.org/functions/system.html): You can check all the failure possibilities by inspecting $? like this: `if ($? == -1) { print "failed to execute: $!\n"; } elsif ($? & 127) { printf "child died with signal %d, %s coredump\n", ($? & 127), ($? & 128) ? 'with' : 'without'; } else { printf "child exited with value %d\n", $? >> 8; }` [download] I'm curious as to what determines the use of 127 and 128 in this script, and what is meant by "$? >> 8"? Thanks!	[reply] [d/l]
Re^3: Boolean (was Boolian) operators defy my understanding... by ikegami (Patriarch) on Jun 21, 2007 at 17:33 UTC
I'm curious as to what determines the use of 127 and 128 in this script The format of `system`'s return value. `system` returns either -1, or a (at least) 32-bit value composed of three fields. `bit F E D C B A 9 8 7 6 5 4 3 2 1 0 +---------------+-+-------------+ \|xxxxxxxxxxxxxxx\|c\|sssssssssssss\| +---------------+-+-------------+` [download] s: Signal that caused the child to exit or 0 if the child existed normally. c: A core dump was produced if 1. x: Child's exit code (if s is zero). what is meant by "$? >> 8"? Perl operators are documented in perlop.	[reply] [d/l] [select]