$string =~ / \w/;  # a space followed by a word character
$string =~ /\s\w/; # any whitespace character followed by a word character
$string =~ /\s\S/; # any whitespace character followed by a non-whitespace character

##</code><code>##

#!/usr/bin/env perl
use 5.010; use strict; use warnings;

my @s = ('John', 'John ', 'John Doe', 'John P. Doe'); # last 2 should match
for (@s){
  my @v = split /\s+\b/;  # split on whitespace followed by a word boundary
  if(@v > 1 ){           # if the split did any splitting
    say;                 # do stuff with the line or elements
  }
}

##</code><code>##

                 Rate split and check check and split
split and check 145/s              --             -1%
check and split 146/s              1%              --

##</code><code>##

                 Rate check and split split and check
check and split 112/s              --            -17%
split and check 136/s             21%              --

##</code><code>##

#!/usr/bin/env perl
use 5.010; use strict; use warnings;
use Benchmark qw(:all);
use Data::Printer;

# my @s = ('John', 'John ', 'John Doe', 'John P. Doe') x 1000; # big array 50% need split
my @s = ('John', 'John Poe', 'John Doe', 'John P. Doe') x 1000; # big array 75% need split

cmpthese( 1000, {
	'split and check'  => \&one,
	'check and split'  => \&two,
});

sub one {
    for (@s){
        my @v = split /\s+\b/;  # split on a space followed by a word boundary
        if($v[1] ){             # if the split did any splitting
                                # do stuff with the line or elements
        }
    }
}

sub two {
    for (@s){
        if (/\s\b/){               # if the line would be split
            my @v = split /\s+\b/; # split it
                                   # do stuff with the line or elements
        }
    }
}