May not be the best practise in the world, but this works like you asked.

'foo' returns array, and 'if' statement looks like

    if ((($r,$m) = foo($i))[0]) {
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Example:

#!/usr/bin/perl
use strict;
my ($m, $r);

foreach my $i (1 .. 2) {

    print "\n";
    if ((($r,$m) = foo($i))[0]) {
        print "It worked\n";
    }
    else {
        print "error: $m\n";
    }
}

sub foo {
    my $num = shift;
    my @ret = ();
    if ($num == 1){
        print "inside foo, good\n";
        @ret = ($num,"good input number");
    }
    else {
        @ret = (0,"bad input number");
    }
    return @ret;
}
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