Softpanorama (slightly skeptical) Open Source Software Educational Society

May the source be with you, but remember the KISS principle ;-)

Perl Tips/Snippets

1. Dynamic activation of the debugger (from Perl debugged):

   while (<INPUT>)
      {
      $DB::trace = 1, next if /debug/;
      $DB::trace = 0, next if /nodebug/;
      # more code
      }

   When run under the debugger, this enables tracing when the loop encounters an input line containing "debug" and ceases tracing upon reading one containing "nodebug". You can even force the debugger to breakpoint by setting the variable $DB::single to 1, which also happens to provide a way you can debug code in BEGIN blocks (which otherwise are executed before control is given to the debugger).
    

2. Sometimes it makes sense to use regular expressions instead of substr. One such task is extraction of component of date, for example:

   $cur_date='20060325';

   (year, $month, $day)=$cur_date=~/(\d{4})(\d\d)(\d\d)/;

3. Perl cross-reference reports. The B::Xref module can be used to generate cross-reference reports for
   Perl programs.
   
   perl -MO=Xref[,OPTIONS] scriptname.plx
    

4. Setting a value of parameter to default value

   # --- process the second parameter 
   $msglevel=($ARGV[1]) ? $ARGV[1] : $msglevel; # defaults is the three digit constant(see below)
   ($msglevel1, $msglevel2, $testing) = split(//,$msglevel); # get flags

5. Creating timestamp

   # Timestamp
   #
   ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst)=localtime(time);
   $year+=1900;
   $mon++;
   for ($mon, $mday, $hour, $min, $sec) {
   	if (length($_)==1) {
   		$_="0$_";
   	}
   } 

6. Move via link/unlink (should be the same filesystem)

   link($_[0], $target);
   if (-e $target) {
   unlink($_[0]);
   } else {
   logger("SFail to move the file '$_[0]' to '$home/$_[1]/$target' \n");
   return;
   }

7. Removing duplicates: here the second part will be executed only if $new{$match} is still undefined:

   if ( $new{$match}++ || !( $tags{$match} = sprintf( "%s\t%s\t?^%s\$?\n", $match, $ARGV, $_ ) ) )

Recommended Links

oreilly.com -- Online Catalog Perl Cookbook Chapter 8: File Contents (HTML Format)

Dekan's Solace - Perl Tips

Perl tricks and tips

Last updated: October 11, 2008