CMPS 335 Advanced Web Publishing Perl and CGI Programming


Subroutines

Individual statements are often gouped into logical units called procedures.  There are two major types of procedures used in Perl: functions and subroutines.  In general, system-defined procedures are called functions and user-defined procedures are subroutines.  A subroutine may have operands called arguments or parameters.  Arguments are usually enclosed in parentheses and are separated by commas if there are more than one.  Like functions, a subroutine also has an intrinsic final value called a return value.  The return value can be stored for later use.  The default return value is the value of the last expression evaluated.

Subroutines are reusable programs that can be used as many times as needed simply by referring to their names.  Subroutines are extremely useful time-saving devices in programming.  Typical subroutines for CGI scripts do common tasks such as parsing forms and printing out HTML headers.  The Parse_Form script performs important form-parsing task and is used as a subroutine in many other Perl scripts.

The Parse_Form subroutine 
  sub Parse_Form {

  if ($ENV{'REQUEST_METHOD'} eq 'GET') {
    @pairs = split(/&/, $ENV{'QUERY_STRING'}); 
  } 
  elsif ($ENV{'REQUEST_METHOD'} eq 'POST') {
    read (STDIN, $buffer,  $ENV{'CONTENT_LENGTH'});
    @pairs = split(/&/, $buffer);

      if ($ENV{'QUERY_STRING'}) {
        @getpairs = split(/&/,  $ENV{'QUERY_STRING'});
        push(@pairs,@getpairs);
      }
  }
  else {
    print "Content-type: text/html\n\n";
    print "<br>Use POST or GET";
    }

  foreach $pair (@pairs) {
    ($key, $value) = split (/=/, $pair);
    $key =~ tr/+/ /;
    $value =~ tr/+/ /;
    $key =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
    $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg; 
    $value =~s///g;

  if ($formdata{$key}) {
    $formdata{$key} .= ", $value";
  } else {
    $formdata{$key} = $value;
  }
  }
  }   
  1;


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