and it might be a good idea to check the return value of your open call open (FILE, "<$footer") or die "Couldn't open file $footer: $!";

Apart from that, it might not be necessary to read the whole file into memory. So you could do something like 

open (FILE, "<$footer") or die "Couldn't open file $footer: $!";

while (my $line = <FILE>) {
  $line =~ s/something/something_else/g;
  
  # print changed line
  print $line;

  # do some very complicated other stuff here
}
close FILE;

[download]
But this depends strongly on what you are doing with the lines of the file.

Update: Added comment pointing to more complex operations in while loop.

Thanks davorg, I was aware of your command line solution. Nevertheless I posted in order to stress the fact that there is the while-loop alternative to the memory intensive 'map on array' which was suggested by jj808 and ChemBoy. And I assumed that Kage wanted to do a little bit more than just printing the changed line - although my short snippet didn't show that :)

-- Hofmator

In reply to Re: How can I make a regex apply to each line of a file? by Hofmator
in thread How can I make a regex apply to each line of a file? by Kage

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.