Please explain this Perl code

Factual Questions
1

I found this giblet of perl in a folder on the website that i am taking over at work. Not being a programmer or scripter, i cannot really understand what it is trying to do or whether i want to find out. So i ask if someone would be able to translate for me:



#!/usr/bin/perl -w
use CGI qw(:standard);

($volume) = @ARGV;
#! EDIT THE NEXT TWO LINES ONLY - SEE README FILE FOR INSTRUCTIONS
my $idxroot = "/Inetpub/wwwroot/ccgh/";	  #path of server
my $docroot = "http://www.myserver.com/"; #location (URL) of server (REPLACE www.myserver.com with the name of your web server)
#! DO NOT EDIT ANYTHING BELOW THIS LINE

my $searchkey = param("find");		       #search field from input form
open(INDEX, $idxroot . $volume . "gob.idx") || die "Can't open: $!";
$title = <INDEX>; #use first line of index file for title

print <<End_start;
Content-type: text/html

<html>
<head><TITLE>$title
</TITLE></head>
<BODY bgcolor=#FFFFFF>
<h3><center>$title
</center></h3></head>
<HR size=3>
<h4><em>Search Results for <u>$searchkey</u>:</em></h4>
<table cellspacing=5><tr>
End_start

if ($searchkey){
  @hdrs = split /~/, <INDEX>;
  $ncol=@hdrs;
  for($i=1; $i<$ncol; $i++) {
    print "<th valign=bottom>$hdrs[$i]<hr></th>";
  }
  print "</tr>
";

#Take care of wildcards in ICD-9 codes:
  if($searchkey=~/\.[0-9xX\*\?\+][0-9xX\*\?\+]/){ #Found two decimal places
   $searchkey =~ s/[xX\*\?\+]/\\w\*/g; #replace wildcard with PERL wildcard 
   $searchkey =~ s/\.([0-9])/\.\[\1xX\]/; #replace first decimal place with that digit or an X
   $searchkey =~ s/([0-9]$)/\[\1xX\]/; #replace last decimal place with that digit or an X
   $searchkey =~ /\Q$searchkey\E/; #precede non-alpha numeric characters with a backslash
  }
  elsif ($searchkey=~/\.[0-9xX\*\?\+]/){ #Found one decimal place
   $searchkey =~ s/[xX\*\?\+]/\\w\*/; 
   $searchkey =~ s/\.([0-9])/\.\[\1xX\]\\w\*/; 
   $searchkey =~ /\Q$searchkey\E/; 
  }
  elsif ($searchkey=~/\./){ #Found a period in searchkey
   $searchkey =~ s/\.//; #Remove it from searchkey
  }
  while(<INDEX>){
    if(/\b$searchkey/i){ #Found match (allow partial words)
      $count++;
      @fields = split(/~/); 
      print "<tr><td valign=top><a href=".$docroot.$volume.$fields[0].">$fields[1]</a></td>";
      for($i=2; $i<$ncol; $i++) {
	print "<td valign=top>".$fields[$i]."</td>";
      }
      print "</tr>
"; 
    }
  }
} #End of if($searchkey)
if(!$count){
  print "<p>No Matches Found</p>";
}
print <<All_Done;
</table>
</BODY>
</html>
All_Done
2

It’s a CGI script that takes a keyword and searches an index for it. The first few lines (up until the “print” statement) open the index file gob.idx and get the keyword from the HTTP query. The next few lines print out some HTML. Then it does some rewriting of the keyword, probably to make sure it’s in the right format, and does a brute force loop over the index, looking for lines that match the keyword. It prints those out into an HTML table.

HTH