I can answer the first for you. m// matches the nothing at any part of the string: 
my $target = 'this is a test of the servise';
$target =~ s//are/;
print "$target\n";

[download]
There's a spot of nothing at the very start of the string.

I think you're missing /g at the end of the regex in the loop condition. As for that, my assumption is that there's Deep Magic here, and you shouldn't rely on these results.

Another test: 

if ($target =~ /test/) {
    $target =~ s//quiz/;
}

[download]
Maybe a blank regex condition on the left stays with what was previously matched. Dunno if that's an intended feature or not.

Update: I'm upgrading it to potential bug: 

my $target = 'this is a test of the servise';

if ($target =~ /test/) {
    $target =~ s//test2/;
}

if ($target =~ /nothing/) {
    $target = s//null/;
} else {
    $target =~ s//foo/;
}

[download]
The moral of the story is, don't do a substitution inside a match on the same string.

In reply to Re: s/// operator and undef question... by chromatic
in thread s/// operator and undef question... by ismail

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