That's roughly how I would have done it, except that :decoding(UTF-8) is wrong, it's still :encoding(UTF-8).

Here is a working example how to search for that character:

use strict;
use warnings;
use charnames qw(:full);

binmode STDOUT, ':encoding(UTF-8)';
my $filename = 'test.txt';

if (@ARGV) {
    open my $handle, '>:encoding(UTF-8)', $filename
        or die "Can't write to file '$filename': $!";
    print $handle <<"OUT";
The next line
contains a\N{MODIFIER LETTER GLOTTAL STOP}
Really!
OUT
    close $handle or warn $!;
} else {
    open my $handle, '<:encoding(UTF-8)', $filename
        or die "Can't open file '$filename' for reading: $!";
    for (<$handle>) {
        print if /\N{MODIFIER LETTER GLOTTAL STOP}/;
    }
    close $handle;
}
[download]

When you call it with command line arguments it writes a test file, when called without any that test file is read again:

$ perl sample.pl gen
$ perl sample.pl 
contains aˀ

I hope this help, you can gradually morph it into the program you want, when you change something and it breaks you know what's wrong.