$ catfiles.pl *.txt *.html > mynewfile.txt

##</code><code>##

#!/usr/bin/perl
use strict; use warnings;
local $|=1; #turn of buffering

for ( map { glob $_ } @ARGV ) {
    open my $FH, '<', $_ or do {
        warn "Can't open '$_' for read, skipping: $!";
        next;
    }
    while (<$FH>) { print $_ }
    close $FH;
}