my $Usage = "Usage:  $0  infile  outfile\n";

# open input and output files
die $Usage unless ( @ARGV == 2 );

open( IN, $ARGV[0] ) or die "Unable to read $ARGV[0]: $!\n$Usage";
open( OUT, ">$ARGV[1]" ) or die "Unable to write $ARGV[1]: $!\n$Usage";

...

##</code><code>##

converter.pl < some.input > some.output
# or
some_process | converter.pl | another_process
# or any combination of the above...

##</code><code>##

while (<IN>) {
    my @chars = split //;
    for (@chars) {   # $_ now holds one char per iteration
        my $out = ( exists $name{$_} ) ?  $name{$_} : $_;
        print $out;
    }
}