use strict;
use warnings;
my $string  
    = 'field1 '
    . 'field2 '
    . 'field3 '
    . 'field4 '
    . 'field5 '
    . 'field6 '
    . 'field7 '
    . 'field8 '
    . 'field9 '
    . 'file name here '
    . 'field11 '
    . 'field12 '
    . 'field`3 '
    . 'field14 '
    . 'field15 '
    . 'field16 '
    . 'field17 '
    . 'field18 '
    . 'field19'
    ."\n"
    ;
my $skip_field = qr /[^\s]+\s+/; # Include any non-whitspace character
my $file_field = qr /[\w\s]+/;   # Include word characters and spaces
my ($file_name)
    = $string =~ m/\A$skip_field{9}($file_field)\s$skip_field{9}\z/;

print $file_name, "\n";