Perl Cookbook

Program: fixstyle

Imagine you have a table with both old and new strings, such as the following.

Old Words	New Words
bonnet	hood
rubber	eraser
lorry	truck
trousers	pants

The program in Example 1.4 is a filter that changes all occurrences of each element in the first set to the corresponding element in the second set.

When called without filename arguments, the program is a simple filter. If filenames are supplied on the command line, an in-place edit writes the changes to the files, with the original versions safely saved in a file with a ".orig" extension. See Section 7.9 for a description. A -v command-line option writes notification of each change to standard error.

The table of original strings and their replacements is stored below __END__ in the main program as described in Section 7.6. Each pair of strings is converted into carefully escaped substitutions and accumulated into the $code variable like the popgrep2 program in Section 6.10.

A -t check to test for an interactive run check tells whether we’re expecting to read from the keyboard if no arguments are supplied. That way if the user forgets to give an argument, they aren’t wondering why the program appears to be hung.

Example 1-4. fixstyle

#!/usr/bin/perl -w # fixstyle - switch first set of <DATA> strings to second set # usage: $0 [-v] [files ...] use strict; my $verbose = (@ARGV && $ARGV[0] eq '-v' && shift); if (@ARGV) { $^I = ".orig"; # preserve old files } else { warn "$0: Reading from stdin\n" if -t STDIN; ...