How to have OS specific code sections in Perl

perltux has asked for the wisdom of the Perl Monks concerning the following question:

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Re: How to have OS specific code sections in Perl by VinsWorldcom (Prior) on Oct 31, 2012 at 17:03 UTC
There error is happening because the module MIDI::ALSA is not installed on your Windows machine. use doesn't work the way you're thinking it does. It is not evaluated as the code is run, but before that. So your "logic" is correct, but your logic is wrong - if that makes sense ;-) There have been many suggestions on how to do this with the if pragma for example, but I've found this to work for me: `use strict; use warnings; my $HAVE_MIDI_ALSA = 0; eval "use MIDI::ALSA"; if($@) { print "MIDI::ALSA required\n"; exit } else { $HAVE_MIDI_ALSA = 1 } if (($^O eq 'linux') and $HAVE_MIDI_ALSA) { 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]	[reply] [d/l]
Re^2: How to have OS specific code sections in Perl by perltux (Monk) on Oct 31, 2012 at 17:38 UTC
Thanks for the explanation as to why my logic is wrong. :-)	[reply]
Re: How to have OS specific code sections in Perl by toolic (Bishop) on Oct 31, 2012 at 17:14 UTC
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'	[reply] [d/l]
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 $LINUX, 'MIDI::ALSA' => ('SND_SEQ_EVENT_PORT_UNSUBSCRIBED', 'SND_SEQ_EVENT_SYSEX'); Can't locate MIDI/ALSA.pm in @INC (@INC contains: /home/aitap/perl5/li +b/perl5/i486-linux-gnu-thread-multi-64int /home/aitap/perl5/lib/perl5 +/i486-linux-gnu-thread-multi-64int /home/aitap/perl5/lib/perl5 /etc/p +erl /usr/local/lib/perl/5.14.2 /usr/local/share/perl/5.14.2 /usr/lib/ +perl5 /usr/share/perl5 /usr/lib/perl/5.14 /usr/share/perl/5.14 /usr/l +ocal/lib/site_perl .) at /usr/share/perl/5.14/if.pm line 13. BEGIN failed--compilation aborted at - line 3. [download] Sorry if my advice was wrong.	[reply] [d/l] [select]
Re^3: How to have OS specific code sections in Perl by perltux (Monk) on Oct 31, 2012 at 19:02 UTC
Thank you, that explains why I had to use: `use if ($^O eq 'linux'), 'MIDI::ALSA'` and why any other alternative with $LINUX I tried didn't work!	[reply] [d/l]
Re^2: How to have OS specific code sections in Perl by perltux (Monk) on Oct 31, 2012 at 17:36 UTC
Thanks, this works great (apart from the second 'use' after the comma in the 'use if' line which is incorrect) and does exactly what I wanted!	[reply]
Re^3: How to have OS specific code sections in Perl by toolic (Bishop) on Oct 31, 2012 at 17:43 UTC
You're welcome. Thanks for pointing out the copy'n'paste error; I updated the post to delete it.	[reply]
Re^2: How to have OS specific code sections in Perl by perltux (Monk) on Oct 31, 2012 at 18:43 UTC
The 'use if' line seems to work only if written as follows: `use if ($^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...	[reply] [d/l]
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]
Re^3: How to have OS specific code sections in Perl by tobyink (Canon) on Oct 31, 2012 at 18:44 UTC
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'`	[reply] [d/l] [select]
Re^3: How to have OS specific code sections in Perl by Anonymous Monk on Nov 01, 2012 at 00:56 UTC
Re^3: code that runs (and works) on both Linux and Win32, Devel::AssertOS, Devel::CheckOS, Re: mention a non-installed module in script, Perl::OSType, Module::Loaded `use if eval { require MIDI::ALSA; MIDI::ALSA->VERSION > 0.01; 1 } , 'M +IDI::ALSA', ...; use if not exist $INC{'MIDI/ALSA.pm'}, 'something::else', ...;` [download]	[reply] [d/l]
Re: How to have OS specific code sections in Perl by choroba (Cardinal) on Oct 31, 2012 at 17:14 UTC
See if. لսႽ� ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply]