use strict;
use warnings;

my $string = '1234 this is the remaining string';

# A4 = take the first 4 ASCII characters
#  x = skip the next byte
# A* = take all remaining ASCII characters
my ( $num, $text ) = unpack( 'A4xA*', $string );

print "[$num][$text]\n";

##</code><code>##

[1234][this is the remaining string]

##</code><code>##

use strict;
use warnings;

use Benchmark qw( cmpthese );

my $string = '1234 this is the remaining string';

cmpthese( -5, {
                unpack => sub { unpack( 'A4xA*', $string ) },
                regex  => sub { $string =~ m[(\d+)\s+(.*)$] },
                split  => sub { split( /(\d+)\s+/, $string, 2 ) },
              } );

##</code><code>##

            Rate  split  regex unpack
split   789472/s     --   -44%   -70%
regex  1422218/s    80%     --   -45%
unpack 2594984/s   229%    82%     --