On a unix system: 
grep 'gateway' infile > outfile

[download]
On a unix system: 
perl -ne'print if /gateway/' infile > outfile

[download]
On a Windows system: 
perl -ne"print if /gateway/" infile > outfile

[download]

An example using file handles: 

# Usage: script.pl infile outfile
# or
# Usage: perl script.pl infile outfile

use strict;
use warnings;

my ($qfn_in, $qfn_out) = @ARGV;

open(my $fh_in, '<', $qfn_in)
   or die("Unable to read file \"$qfn_in\": $!\n");

open(my $fh_out, '>', $qfn_out)
   or die("Unable to create file \"$qfn_out\": $!\n");

while (<$fh_in>) {
   if (/gateway/) {
      print $fh_out $_;
   }
}

[download]

Update: Fixed copy & paste error mentioned in reply.
Update: Must have been asleep! Fixed missing my mentioned in reply.

In reply to Re: search and extract lines which contain a word by ikegami
in thread search and extract lines which contain a word by m@cky

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.