in reply to How to have OS specific code sections in Perl

if (untested): 
use warnings;
use strict;

my $LINUX = 0;

if ($^O eq 'linux') { $LINUX=1; };

use if $LINUX, 'MIDI::ALSA' => ('SND_SEQ_EVENT_PORT_UNSUBSCRIBED',
                               'SND_SEQ_EVENT_SYSEX');

if ($LINUX) {
    print STDERR "OS is Linux\n";
    MIDI::ALSA::client('test',1,1,1);
    MIDI::ALSA::connectfrom(0,'MidiSport 4x4:0');
    MIDI::ALSA::connectto(1,'MidiSport 4x4:0');
    MIDI::ALSA::start();
}

[download]

UPDATE: deleted 2nd 'use'

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Re^2: How to have OS specific code sections in Perl
by aitap (Curate) on Oct 31, 2012 at 18:54 UTC
    Unfortunately, this is not going to work because $LINUX is undef at compile-time: 
    $ perl 
if ($^O eq 'linux') { $LINUX=1; };

use if $LINUX, 'MIDI::ALSA' => ('SND_SEQ_EVENT_PORT_UNSUBSCRIBED',
                               'SND_SEQ_EVENT_SYSEX');
__END__
$ perl -MMIDI::ALSA
Can't locate MIDI/ALSA.pm in @INC (@INC contains: /home/aitap/perl5/li
+b/perl5/i486-linux-gnu-thread-multi-64int /home/aitap/perl5/lib/perl5
+/i486-linux-gnu-thread-multi-64int /home/aitap/perl5/lib/perl5 /etc/p
+erl /usr/local/lib/perl/5.14.2 /usr/local/share/perl/5.14.2 /usr/lib/
+perl5 /usr/share/perl5 /usr/lib/perl/5.14 /usr/share/perl/5.14 /usr/l
+ocal/lib/site_perl .).
BEGIN failed--compilation aborted.

    [download]
    But if the test is done in the BEGIN{} section, everything works (well, not for me because of the absence of the module): 
    $ perl 
BEGIN{ if ($^O eq 'linux') { $LINUX=1; }; }
use if $LINUX, 'MIDI::ALSA' => ('SND_SEQ_EVENT_PORT_UNSUBSCRIBED',
                               'SND_SEQ_EVENT_SYSEX');
Can't locate MIDI/ALSA.pm in @INC (@INC contains: /home/aitap/perl5/li
+b/perl5/i486-linux-gnu-thread-multi-64int /home/aitap/perl5/lib/perl5
+/i486-linux-gnu-thread-multi-64int /home/aitap/perl5/lib/perl5 /etc/p
+erl /usr/local/lib/perl/5.14.2 /usr/local/share/perl/5.14.2 /usr/lib/
+perl5 /usr/share/perl5 /usr/lib/perl/5.14 /usr/share/perl/5.14 /usr/l
+ocal/lib/site_perl .) at /usr/share/perl/5.14/if.pm line 13.
BEGIN failed--compilation aborted at - line 3.

    [download]
    Sorry if my advice was wrong.
[reply]
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[select]
      Thank you, that explains why I had to use:

      use if ($^O eq 'linux'), 'MIDI::ALSA'

      and why any other alternative with $LINUX I tried didn't work!
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Re^2: How to have OS specific code sections in Perl
by perltux (Monk) on Oct 31, 2012 at 17:36 UTC
    Thanks, this works great (apart from the second 'use' after the comma in the 'use if' line which is incorrect) and does exactly what I wanted!
[reply]
      You're welcome.

      Thanks for pointing out the copy'n'paste error; I updated the post to delete it.

[reply]
Re^2: How to have OS specific code sections in Perl
by perltux (Monk) on Oct 31, 2012 at 18:43 UTC
    The 'use if' line seems to work only if written as follows:

    use if ($^O eq 'linux'), 'MIDI::ALSA' => ('SND_SEQ_EVENT_PORT_UNSUBSCR
+IBED',
                                          'SND_SEQ_EVENT_SYSEX');

    [download]

    Any other way to write the 'use if' CONDITION doesn't seem to work.
    Weird...
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Re^2: How to have OS specific code sections in Perl
by perltux (Monk) on Oct 31, 2012 at 18:00 UTC
    Actually unfortunately I spoke to soon, the code now works fine in Windows (no errors anymore) but now I get an error in Linux:

    Undefined subroutine &MIDI::ALSA::client called at ./test.pl line 15

    It looks like the 'use if' line needs some more tweaking to work correctly, but how?
[reply]

      The problem is that the conditional block is only evaluated at run time, by which time it's too late for use if.

      You want:

      my $LINUX;
BEGIN { $LINUX = ($^O eq 'linux') };
use if $LINUX, 'MIDI::ALSA' => ('SND_SEQ_EVENT_PORT_UNSUBSCRIBED', 'SN
+D_SEQ_EVENT_SYSEX');

      [download]

      Or better:

      use if ($^O eq 'linux'), 'MIDI::ALSA' => ('SND_SEQ_EVENT_PORT_UNSUBSCR
+IBED', 'SND_SEQ_EVENT_SYSEX');

      [download]
      perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'
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[d/l]
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