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Learning Perl, 5th Edition
book

Learning Perl, 5th Edition

by Randal L. Schwartz, Tom Phoenix, brian d foy
June 2008
Beginner content levelBeginner
352 pages
11h 16m
English
O'Reilly Media, Inc.
Content preview from Learning Perl, 5th Edition

Option Modifiers

There are several option modifier letters, sometimes called flags, which may be appended as a group right after the ending delimiter of a regular expression to change its behavior from the default.

Case-Insensitive Matching with /i

To make a case-insensitive pattern match, so you can match FRED as easily as fred or Fred, use the /i modifier:

print "Would you like to play a game? ";
chomp($_ = <STDIN>);
if (/yes/i) {  # case-insensitive match
  print "In that case, I recommend that you go bowling.\n";
}

Matching Any Character with /s

By default, the dot (.) doesn’t match newline, and this makes sense for most “look within a single line” patterns. If you might have newlines in your strings, and you want the dot to be able to match them, the /s modifier will do the job. It changes every dot[*] in the pattern to act like the character class [\d\D] does, which is to match any character, even if it is a newline. Of course, you have to have a string with newlines for this to make a difference:

$_ = "I saw Barney\ndown at the bowling alley\nwith Fred\nlast night.\n";
if (/Barney.*Fred/s) {
  print "That string mentions Fred after Barney!\n";
}

Without the /s modifier, that match would fail, since the two names aren’t on the same line.

Adding Whitespace with /x

The third modifier you’ll see allows you to add arbitrary whitespace to a pattern to make it easier to read:

/-?\d+\.?\d*/         # what is this doing?
/ -? \d+ \.? \d* /x   # a little better

Since the /x allows whitespace inside the pattern, ...

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Publisher Resources

ISBN: 9780596520106Supplemental ContentErrata Page