Perl Cookbook

Controlling Case

Problem

A string in uppercase needs converting to lowercase, or vice versa.

Solution

Use the lc and uc functions or the \L and \U string escapes.

use locale;                     # needed in 5.004 or above

$big = uc($little);             # "bo peep" -> "BO PEEP"
$little = lc($big);             # "JOHN"    -> "john"
$big = "\U$little";             # "bo peep" -> "BO PEEP"
$little = "\L$big";             # "JOHN"    -> "john"

To alter just one character, use the lcfirst and ucfirst functions or the \l and \u string escapes.

$big = "\u$little";             # "bo"      -> "Bo"
$little = "\l$big";             # "BoPeep"    -> "boPeep"

Discussion

The functions and string escapes look different, but both do the same thing. You can set the case of either the first character or the whole string. You can even do both at once to force uppercase on initial characters and lowercase on the rest.

The use locale directive tells Perl’s case-conversion functions and pattern matching engine to respect your language environment, allowing for characters with diacritical marks, and so on. A common mistake is to use tr/// to convert case. (We’re aware that the old Camel book recommended tr/A-Z/a-z/. In our defense, that was the only way to do it back then.) This won’t work in all situations because when you say tr/A-Z/a-z/ you have omitted all characters with umlauts, accent marks, cedillas, and other diacritics used in dozens of languages, including English. The uc and \U case-changing commands understand these characters and convert them properly, at least when you’ve said use locale