So I would say that any code that *sets* $_ is, by definition, wrong.
Unnecessary, perhaps, but not wrong. Setting $_ can be useful:
  1. As a topicalizer in a single-item for loop, to make a series of operations on a common value read more cleanly.

    Instead of this: 

    $h->{foo}{bar} =~ s/[._]/ /g;
Some::Custom::Function($h->{foo}{bar});
$h->{foo}{bar} =~ s/^\s+//;
$h->{foo}{bar} =~ s/\s+$//;
$h->{foo}{bar} =~ s/`/'/g;

    [download]
    You can write this: 
    for ($h->{foo}{bar}) {
    s/[._]/ /g;
    Some::Custom::Function($_);
    s/^\s+//;
    s/\s+$//;
    s/`/'/g;
};

    [download]

  2. And the occasional weird circumstance, like conveniently modifying the values of a hash: 
    map { $_ = foo( $bar, $_ ) } values %somehash;

    [download]
On the other hand, where real for loops are concerned, I find it reduces confusion to always provide your own lexical topic (e.g.  for my $key (@keys) { ... } ). A bit backwards from the way the language is designed, I suppose.

In reply to Re^2: "$_" vs. $_ by mrpeabody
in thread "$_" vs. $_ by argv

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