use Perl

Thanks rafael.   I was just looking for a way to compare files as strings and found File::Compare a bit lacking.

Looks like someone else besides me would like an option to ignore differences in number of whitespaces.   Other options I often use with the Unix diff utility include those to

• ignore differences between lower- and upper-case letters, and
• expand tabs to whitespace.

I suppose I could preprocess the strings before handing them off to is_string():

use Text::Tabs;
use Test::More tests => 1;
use Test::LongString;

# Apply one or more filters.
# N.B. The order in which the filters are applied matters:

my @strings =
    map {tr/\n\r\f / /s; $_}
    map expand($_) =>
    map lc($_)     =>
    <DATA>;

is_string(
    $strings[0],
    $strings[1],
    'Actually differs by one char'
);

__DATA__
This is a test of Test::LongStrings
this    is a    test     of Test::longstring

As far as the _common_prefix_length function is concerned, perhaps using substr would be a bit faster?

     while (length($x) && length($y)) {
-       my ($x1,$x2) = $x =~ /(.)(.*)/s;
-       my ($y1,$y2) = $y =~ /(.)(.*)/s;
+        my $x1 = substr($x, 0, 1, '');
+        my $y1 = substr($y, 0, 1, '');
        if ($x1 eq $y1) {
-           $x = $x2;
-           $y = $y2;
            ++$r;
        }