[oak perl] Regular Expressions

[Belden Lyman]

On Wed, 2004-03-10 at 12:55, Tony Stubblebine wrote:
> Thanks George.
> 
> I'm curious to see what sort of regular expressions people are writing, 
> good and bad. And I'd love to start a discussion on regex style or 
> technique.
> 

I wanted to find all 2 letter words in /usr/dict/words, so cut over
to Perl after finding myself a few pipes deep:

    $ grep '^..$' /usr/dict/words | grep -v '[A-Z][A-Z]' | grep -i '[aeiouy]'

So long as I was doing this in Perl, I decided to make the program find
all N-length words, with N defaulting to 2.

If this looks like an exercise for someone learning (?=) and (?!),
there's a reason for that ;)

    #!/usr/bin/perl -s
    
    use strict;
    use warnings;
    
    our $length;
    $length = 2 unless $length;
    
    @ARGV = '/usr/dict/words';
    
    print grep {
                m/
                 (?=^[A-Za-z]{$length}$)  # entry must be $length letters long
                 (?!^[A-Z]+$)             # ignore all-caps words
                 (?i-:                    # this next part is case insensitive:
                   (?:                    #    we must have either
                     [aeiouy].            #      a vowel, then any letter
                     |                    #      or
                     .[aeiouy]            #      any letter, then a vowel
                   )
                 )
                /xo
               }
               (<>);
    
    __END__

Belden