How can I capitalize the first letter of each word in a string in Perl?

Take a look at the ucfirst function.

$line = join " ", map {ucfirst} split " ", $line;

As @brian is mentioning in the comments the currently accepted answer by @piCookie is wrong!

$_="what's the wrong answer?";
s/\b(\w)/\U$1/g
print; 

This will print "What'S The Wrong Answer?" notice the wrongly capitalized S

As the FAQ says you are probably better off using

s/([\w']+)/\u\L$1/g

or Text::Autoformat

See the faq.

I don't believe ucfirst() satisfies the OP's question to capitalize the first letter of each word in a string without splitting the string and joining it later.