my $x = "the quick brown fox";
if ($x =~ /n\s*f/) {print "found\n"} #the sequence "n f" matched
    # there was an 'n', and 0 or more spaces, then an 'f'

if ($x =~ /bro\s*w/) {print "found\n"} #the 'bro', then no spaces, 
    # and 'w' match - * says 0 or more, so no space is fine