use warnings;
use strict;

my $max = 0;
while (<>) {
    my $len = length;
    $max = $len if $len > $max;
}
print "$max\n";

##</code><code>##

a
abc
abcdef
abcd
abcde

##</code><code>##

              1         2         3        
     12345678901234567890123456789012345678

##</code><code>##

perl -nE'$l=y///c;$m=$l if$l>$m;END{say$m}' file.txt