in reply to s/// operator and undef question...

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";

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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/;
}

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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/;
}

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

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Re: Re: s/// operator and undef question...
by merlyn (Sage) on Dec 13, 2000 at 05:41 UTC 
    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/; 
}

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    My guess is that this returns this is a foo2 of the servise as documented in perlop: 
                   [....] If the pattern evaluates to the empty
               string, the last successfully executed regular
               expression is used instead. [....]

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    And so my standard admonition about "don't use $1 except in the context of a conditional" would also apply here, since "most recent success" is contextual.

    -- Randal L. Schwartz, Perl hacker

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