use warnings;
use strict;
use feature qw(say);
# use diagnostics;

# say  zip ('ABCDEFGHIJ','abcde');

my $zipped= zip ('ABCDEFGHIJ','abcde');

say $zipped;

sub zip {
     # join "", sort {qq(\L$a) cmp qq(\L$b)} split "", $_[0].$_[1];
     join "", sort { lc $a cmp lc $b} split "", $_[0].$_[1];
}

__END__

##</code><code>##

monks>zip.pl
Unquoted string "zip" may clash with future reserved word at \monks\zip.pl line 6.
say() on unopened filehandle zip at monks\zip.pl line 6.

##</code><code>##

say() on unopened filehandle zip at monks\zip.pl line 6 (#1)
    (W unopened) An I/O operation was attempted on a filehandle that was
    never initialized.  You need to do an open(), a sysopen(), or a socket()
    call, or call a constructor from the FileHandle package.