$ perl -lpe '($_=()=/\s+/g)++'   ## leading
 foo bar
3
$ perl -lpe '($_=()=/\s+/g)++'   ## trailing
foo bar 
3
$ perl -lpe '($_=()=/\s+/g)++'   ## both
 foo bar 
4
$ _

##</code><code>##

$ perl -wle 'print scalar (()=/\S+/g) for "a b c", " a b c", "a b c ", " a b c "'
3
3
3
3
$ _