Question

I’d like perl -cw … to return a non-zero exit status if a compilation warning is emitted.

E.g. suppose a.pm is the file:

use warnings;
asd;

Then perl -cw a.pm reports:

Unquoted string "asd" may clash ...
Useless use of a constant in void context ...
a.pm syntax OK

and the exit status is set to 0. I’d like to be able to detect that compilation warnings were emitted – preferably though setting of the exit status.

Answer 1

Set a warning handler in a BEGIN block (near the top of the script, so this block is parsed before the code that might trigger compile-time warnings), and tweak the exit status in an ENDCHECK block.

use strict;
use warnings;
my $warnings;
BEGIN {
    $SIG{__WARN__} = sub { $warnings++; CORE::warn @_ }
}
$used::only::once = 42;
CHECK {
    if ($^C && $warnings > 0) {
        exit $warnings;
    }
}

The $^C variable is true if and only if you have invoked perl with the -c option.