In the so-called good example, both local $_ could easily have been replaced with my. You gain the readability of a named variable at the tiny cost of having to specify the topic of two operations. 

my @a = map { s/\s*(#.*)?$//g; $_ } <DATA>;

my @b;
while (my $group = shift @a) {
   if ($group =~ m/\D(\d+)-(\d+)(?:\D|$)/) {
      my $range = "$1-$2";
      foreach my $i ($1..$2) {
         (my $addr = $group) =~ s/(\D)$range(\D|$)/$1$i$2/;
         push @a, $addr;
      }
   } else {
      push @b, $group;
   }
}

print join("\n", @b);

[download]

There are cases where using $_ helps, but I don't think this is one of them.

Note: The localization of $1 and $2 is unnecessary. It's already being done by the for.

Note: local $_ doesn't preserve $_ in all situations, unfortunately. for ($var) is a far better way of aliasing $_.

In reply to Re^3: "$_" vs. $_ by ikegami
in thread "$_" vs. $_ by argv

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.