kcaran.com

Things I always need to look up in Perl

Here are some random Perl things I always need to look up:

• Text replacement on a per-file basis

  perl -pi -e 's/\/business\//\/illus\/business.html/' */*.html
  

  
  
  • -p : Iterate over each line of the file
  • -i : Don’t create a backup file
  • -e : Enter one or more lines of script

• Muliple line pattern modifiers:
  

  /s allows wildcards (.) to match a newline. Use this to extend a search beyond a single line.

  /m changes the behavior of ^ and $ so they will match the start and end of any line. /^<h4>/m would match any line that began with an h4 heading tag.

  To explicitly match the start and end of the string, use \A and the EOF character, \z.

  The /s and /m modifiers are not mutually exclusive.

• The break and continue keywords from C are last and next in Perl.

• Use localtime to get the current year (assuming post-2000):

  # Year is the sixth element of the localtime list
  $YEAR = 2000 + (( localtime )[5] % 100);
  

  
  
• Redirecting STDOUT temporarily to a scalar (string)

  # Open a filehandle on a string
  my $scalar_file = '';
  open my $scalar_fh, '>', \$scalar_file
  		or die "Can't open scalar filehandle: $!";
  
  # Select scalar filehandle as default, save STDOUT
  my $ostdout = select( $scalar_fh );
  
  # Unbuffered output
  $| = 1;
  
  # Now, close scalar filehandle and bring back STDOUT
  close( $scalar_fh );
  
  print "ABC\n";
  print "DEF\n";
  print "GHI...\n";
  
  # Bring STDOUT back
  select( $ostdout );
  

  
  
• Slurp an entire file into a scalar:

  open my $text_fh, '<', 'myfile.txt' or die $!;
  my $contents = do { local $/;  <$text_fh> };
  

  
  

• Run a function inside of a double-quoted string:

  my $input = qq|<input type="text" name="email"
  	value="${ \escapeHTML( $email ) }">|;
  

• Use Data::Dumper to display a data structure:

  use Data::Dumper;
  warn "KAC:", Data::Dumper->Dump( [$data_structure], ['*main::data_structure'] );
  

Last Updated: Mon, 21 Dec 2009