I'm stuck trying to figure out why my usage of IPC::Open2 isn't working how I expect.

This works:

perl -e 'package MyPack; sub foo { use IPC::Open2; my ($in, $out); my $pid = open2($out, $in, q[program --unbuffered]); print $in q|some json|; my $result = <$out>; warn "got [$result]\n"; close($in); close($out); waitpid($pid, 0); } 1; package Main; MyPack->foo();'

It prints my expected result in square brackets after taking some time to calculate the result.

But if I have lib/MyPack.pm: 

package MyPack;
sub foo { use IPC::Open2; my ($in, $out); my $pid = open2($out, $in, q
+[program --unbuffered]); print $in q|some json|; my $result = <$out>;
+ warn "got [$result]\n"; close($in); close($out); waitpid($pid, 0); }
1;

[download]

and do:

perl -Ilib -MMyPack -e 'MyPack->foo();'

It returns immediately with an empty result set (json empty square brackets inside my printed square brackets). foo() in both cases is copy/pasted. Why doesn't it work from inside a .pm?

Edit for more: Fully copy/pasting the entire contents of the perl 1 liner that works in to lib2/MyPack.pm, and then calling:

perl -Ilib2 -e 'use MyPack;'

also doesn't work. What can it be about having the code inside a .pm that could stop it working?

Edit for solution: my input json string had single quotes, which behaved differently on the command line and inside a .pl or .pm. Removing the quotes made them both behave the same.

In reply to Why is IPC::Open2 behaving differently in a .pm? by sendu

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