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1.13. Controlling Case
1.13.1. Problem
A string in uppercase needs converting to
lowercase, or vice versa.
1.13.2. Solution
Use
the lc and uc functions or the
\L and \U string escapes.$big = uc($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"
1.13.3. Discussion
The functions and string escapes look different, but both do the same
thing. You can set the case of either just the first character or the
whole string. You can even do both at once to force uppercase
(actually, titlecase; see later explanation) on initial characters
and lowercase on the rest.$beast = "dromedary";
# capitalize various parts of $beast
$capit = ucfirst($beast); # Dromedary
$capit = "\u\L$beast"; # (same)
$capall = uc($beast); # DROMEDARY
$capall = "\U$beast"; # (same)
$caprest = lcfirst(uc($beast)); # dROMEDARY
$caprest = "\l\U$beast"; # (same)
These capitalization-changing escapes are commonly used to make a
string's case consistent:# titlecase each word's first character, lowercase the rest
$text = "thIS is a loNG liNE";
$text =~ s/(\w+)/\u\L$1/g;
print $text;
This Is A Long Line
You can also use these for case-insensitive comparison:if (uc($a) eq uc($b)) { # or "\U$a" eq "\U$b"
print "a and b are the same\n";
}
The randcap program, shown in Example 1-2, randomly titlecases 20 percent of the letters
of its input. This lets you converse with 14-year-old WaREz d00Dz.
Example 1-2. randcap
#!/usr/bin/perl -p
# randcap: filter to randomly capitalize 20% of the letters
# call to srand( ) is unnecessary as of v5.4
BEGIN { srand(time( ) ^ ($$ + ($$<<15))) }
sub randcase { rand(100) < 20 ? "\u$_[0]" : "\l$_[0]" }
s/(\w)/randcase($1)/ge;
% randcap < genesis | head -9
boOk 01 genesis
001:001 in the BEginning goD created the heaven and tHe earTh.
001:002 and the earth wAS without ForM, aND void; AnD darkneSS was
upon The Face of the dEEp. and the spIrit of GOd movEd upOn
tHe face of the Waters.
001:003 and god Said, let there be ligHt: and therE wAs LigHt.
In languages whose writing systems distinguish between uppercase and
titlecase, the ucfirst( ) function (and
\u, its string escape alias) converts to
titlecase. For example, in Hungarian the "dz"
sequence occurs. In uppercase, it's written as "DZ", in titlecase as
"Dz", and in lowercase as "dz". Unicode consequently has three
different characters defined for these three situations:Code point Written Meaning
01F1 DZ LATIN CAPITAL LETTER DZ
01F2 Dz LATIN CAPITAL LETTER D WITH SMALL LETTER Z
01F3 dz LATIN SMALL LETTER DZ
It is tempting but ill-advised to just use
tr[a-z][A-Z] or the like to convert case. This is
a mistake because it omits all characters with diacritical
markings—such as diaereses, cedillas, and accent
marks—which are used in dozens of languages, including English.
However, correctly handling case mappings on data with diacritical
markings can be far trickier than it seems. There is no simple
answer, although if everything is in Unicode, it's not all that bad,
because Perl's case-mapping functions do work perfectly fine on
Unicode data. See the section on The
Universal Character Code in the
Introduction to this chapter for more information.
1.13.4. See Also
The uc, lc,
ucfirst, and lcfirst functions
in perlfunc(1) and Chapter 29 of
Programming Perl; \L,
\U, \l, and
\u string escapes in the "Quote and Quote-like
Operators" section of perlop(1) and Chapter 5 of
Programming Perl
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| 1.12. Expanding Variables in User Input |  | 1.14. Properly Capitalizing a Title or Headline |
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