Re^2: Boolean (was Boolian) operators defy my understanding...

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!

Comment on Re^2: Boolean (was Boolian) operators defy my understanding... Download Code

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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]

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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]