Current Perl documentation can be found at perldoc.perl.org.
Here is our local, out-dated (pre-5.6) version:
Use the split function:
while (<>) { foreach $word ( split ) { # do something with $word here } }
Note that this isn't really a word in the English sense; it's just chunks of consecutive non-whitespace characters.
To work with only alphanumeric sequences, you might consider
while (<>) { foreach $word (m/(\w+)/g) { # do something with $word here } }