1.13.1. Problem

1.13.2. Solution

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

$big = "\u$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";
}

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