Working with Patterns

Overview

• Perl's ability to work with patterns is extensive
• The =~ operator allows matching to be used as an operator
• Built-in regular expression processing allows flexibility in matching
• Built-in functionality from Unix programs such as sed and tr allow familiar transformations
• split makes it easy to divide strings based on patterns
• ... and much much more!

Code snippets

• Basic match syntax:
  if ( $a =~ "hello" ) { .... }
• grep-like behavior:
  print if ( /$var/ );
• tr-like behavior:
  my $b =~ tr/$inpat/$outpat/
• sed-like substitution:
  my $b; $b =~ s/$inpat/$outpat/i (the i makes the match case insensitive)

Regular expressions

• Stuff to read: man perlrequick ... man perlre ... man perlretut
• Detail: Perl doesn't necessarily distinguish between a simple pattern and a regular expression. Also note that patterns might be re-interpreted, even every time through a loop - man perlretut for ways to avoid this.
• Sample: match letters @ start of line:
  print if /^[a-zA-Z]/;
• Sample: splitting input based on whitespace
  

  $x = "Calvin and Hobbes";
  my @word = split /\s+/, $x;  # $word[0] = 'Calvin'
                 # $word[1] = 'and'
                 # $word[2] = 'Hobbes'