Chapter 9. Processing Text with Regular Expressions
You can use regular expressions to change text too. So far we’ve only shown you how to match a pattern, and now we’ll show you how to use patterns to locate the parts of strings that you want to change.
Substitutions with s///
If you think of the
m// pattern match
as being like your word processor’s “search” feature, the “search and
replace” feature would be Perl’s
substitution operator. This simply replaces whatever part of a variable
matches the pattern with a replacement string:
$_ = "He's out bowling with Barney tonight."; s/Barney/Fred/; # Replace Barney with Fred print "$_\n";
m//, which can match
against any string expression,
is modifying data that must therefore be contained in what’s known
lvalue. This is
nearly always a variable, but could be anything you can use on the left side of an
If the match fails, nothing happens, and the variable is untouched:
# Continuing from previous; $_ has "He's out bowling with Fred tonight." s/Wilma/Betty/; # Replace Wilma with Betty (fails)
Of course, both the pattern and the replacement string could be more
complex. Here, the replacement string uses the first capture variable,
$1, which is set by the pattern
s/with (\w+)/against $1's team/; print "$_\n"; # says "He's out bowling against Fred's team tonight."
Here are some other possible substitutions. These are here only as samples; in the real world, it would not be typical to do so many ...