Perl Quick Lab 51 character classes, g option, + quantifier, - | and b meta characters, pattern memory () and $1

Copyright ã1998, 1999 Alonzo L. Hosford, Jr.

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Required: Notepad, MSDOS Prompt, Windows version of Perl, hard drive or floppy disk to save files.

1. Windows: Create a work folder on your hard drive or use a floppy disk as your work folder.

2. Windows: Start Windows Note Pad

3. Notepad: Type the following text.

#!/usr/bin/perl

# regexp17.pl

# regular expressions

# the substitution operator

# meta character \b

# pattern memory

print "Regular expressions\n";

print "Substitution operator s// \n";

print "Use of the g option (global) \n";

print "Use of quantifier + \n";

print "Use of meta character b (word boundary) \n";

print "Use of meta character | (or) \n";

print "Use of character class and range meta character \n";

print "Use of pattern memory variables. In this case \$1 \n";

print "Substitutes all cases of one or more contiguous numbers \n";

print "enclosed in word boundary or one or more contiguous numbers a comma\n";

print "followed by one or more contiguous numbers all enclosed in a word boundary.\n";

print "The match is surrounded by parenthesis.\n\n";

$myline = "About 18 brown baby foxes ran after the 35,499 rabbits at the BBB ranch.";

$_ = $myline;

print "\$_ before = $_\n";

$result = s/\b([0-9]+,[0-9]+|[0-9]+)\b/\($1\)/g;

print "\$_ after = $_\n";

print "expression = \\b([0-9]+,[0-9]+|[0-9]+)\\b\n";

print "replacingText = (\$1)\n";

print "\$result = $result\n";

print "substitutions = $result\n";

4. Notepad: Save in your work folder as regexp18.pl.

5. Windows task bar: Select MSDOS Command Prompt.

6. MSDOS Command Prompt: Test the syntax. Type the following and press the Enter key:

perl regexp18.pl

Example of output:

A:>

perl regexp18.pl

Regular expressions Substitution operator s// Use of the g option (global) Use of quantifier + Use of meta character b (word boundary) Use of meta character | (or) Use of character class and range meta character Use of pattern memory variables. In this case $1 Substitutes all cases of one or more contiguous numbers enclosed in word boundary or one or more contiguous numbers a comma followed by one or more contiguous numbers all enclosed in a word boundary. The match is surrounded by parenthesis. $_ before = About 18 brown baby foxes ran after the 35,499 rabbits at the BBB r anch. $_ after = About (18) brown baby foxes ran after the (35,499) rabbits at the BBB ranch. expression = \b([0-9]+,[0-9]+|[0-9]+)\b replacingText = ($1) $result = 2 substitutions = 2