Here's a basic idea of how I might approach this problem.
  1. Open 1.txt and read its contents into a data structure suitable for later use.
  2. Process each line of 2.txt. Change the line based on the data read in step 1, and write it to a third file.
  3. When processing of 2.txt is complete, rename the third file to 2.txt
Example of step 1: 
my %new_pass;
while (<F1>) {
  chomp;
  my @f = split(':', $_);
  $new_pass{$f[0]} = $f[2];
}

[download]
Example of step 2: 
while (<F2>) {
  chomp;
  my @f = split(':', $_);
  if (exists $new_pass[$f[0]]) {
    $f[1] = $new_pass[$f[0]];
  }
  print F3 join(':', @f), "\n";
}

[download]

In reply to Re: Input Output file by pc88mxer
in thread Input Output file by deep_rastogi

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.