use strict;
use warnings;

opendir DIR, ".";

foreach $file (readdir DIR)
{
   open ( FILE, $file ) or die "Can't open $file: $!\n";
   @lines = <FILE>;
   close FILE;

   # Open same file for writing, reusing STDOUT
   open (FILE, ">$file") or die "Can't open $file: $!\n";

   # Walk through lines...
   foreach $line ( @lines )
   {
      # if line contains x_x_x(), create link & print to file
      if ($line =~ //) 
      {
         # change x_x_x() to <A HREF="x_x_x.html">x_x_x()</A>
      }
      # else print unchanged line to file
      else
      {
         print FILE $line;
      }
   } 
   close FILE;
}

closedir( DIR );