» CS 330 Lecture 3 – Regular expressions++

CS 330 Lecture 3 – Regular expressions++

January 27, 2012 by Chris Johnson. Filed under cs330, lectures, spring 2012.

Agenda

more wildcard characters
developing on clark.cs.uwec.edu
substitution
slurping a file
expressions as replacements
Perl subroutines
zero-width assertions

Code

emails.pl

#!/usr/bin/perl

open($in, '<', 'getlist.txt');

while ($line = <$in>) {
  $line =~ s/^(\S+).*$/$1\@uwec.edu/;
  print($line);
}

close($in);

page.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
   <title></title>
</head>
<body>

<h2>Foo</h2>

<h3>Blech</h3>

<h4>Scrumpt</h4>

</body>
</html>

demote.pl

#!/usr/bin/perl

open($in, '<', 'page.html');

{
  local $/ = undef;
  $html = <$in>;

  $html =~ s#(<\s*/?h)(\d)(\s*)#$1 . ($2 - 1) . $3#gie;
}

print $html;

close($in);

text.txt

asdfasjkdf askjdf asdkjfhadsjkf hasdkjfsad'fasdf
sdf
asfdsafasdfa
sdfas dfsakdjfsakldfj asdf
asdf

asdfasdjf asdfkljasdf kasdhfsakjdhf sadf sadfjhsdajkfhsadjfhsdf asdfj sdfkjhasfd kjasdf 
asdfhasdjkhf 

asdflj asdfl sadf asdlfkja sdf
alsdkjfasdflj asdfasd fasd falsdjfadsf
lasdkjfsaldf asdfhsdfjk

foo

insert_paras.pl

#!/usr/bin/perl

open($in, '<', 'text.txt');

{
  local $/ = undef;
  $html = <$in>;

  $html =~ s#(?<=\n)(?=\n)#</p>\n\n<p>#g;
}

print "<p>$html</p>";

close($in);

stuff.txt

asdf asdfjhasd kfjhasdf
sadfjasdf 
[1, 5, 6]
asdfkjlasd
[10]
[6, 0 , 3]

summer.pl

#!/usr/bin/perl

sub sum($) {
  my($sequence) = @_;
  $sum = 0;
  while ($sequence =~ m/(\d+)/g) {
    $sum += $1;
  }
  return $sum;
}

open($in, '<', 'stuff.txt');

{
  local $/ = undef;
  $html = <$in>;

  $html =~ s#\[(\s*\d+(\s*,\s*\d+)*\s*)\]#sum($1)#ge;
}

print $html;

close($in);

Haiku

interpretation A:
spouse criteria
match caret dot star dollar
I am desperate

interpretation B:
spouse criteria
match caret dot start dollar
all wild, always