root@bbe78e26dc1f:~/rsh# cat memtest-u2a.pl 

#!/usr/bin/env perl
use warnings;
use strict;
use Encode;

my $mem_initial=psmem();
my $mem_last=$mem_initial;

print "INITIAL: $mem_initial\n";

foreach my $cycle (0..($ARGV[0] || 200)) {
    foreach my $i (0..100) {
        my $u="x";

        wtf_leak($u);
        ### wtf_noleak($u);

        ### $u =~ s/\x{2122}/(TM)/sg;
        ### $u =~ s/b/(TM)/sg;
    }

    my $mem=psmem();
    my $usage_total=$mem - $mem_initial;
    my $usage_last=$mem - $mem_last;

    if($usage_last > 0) {
        print "---------------- CYCLE: $cycle, since-last $usage_last, total $usage_total, initial $mem_initial, current $mem\n";
    }

    $mem_last=$mem;
}

my $mem=psmem();
my $usage_total=$mem - $mem_initial;
print "FINAL: $mem, LEAKED $usage_total\n";

exit 0;

##############################################################

sub psmem {
    ### chomp(my $mem=`ps -h -o rss -p $$`);
    chomp(my $mem=`ps -h -o vsz -p $$`);
    ### dprint "mem=$mem";
    return 0 + $mem;
}

# Leaks memory!
#
sub wtf_leak {
    my $text=shift;

    $text =~ s/\x{2122}/(TM)/sg;

    return $text;
}

# DOES NOT leak memory!
#
my $retm;

sub wtf_noleak {
    my $text=shift;

    $retm||=Encode::encode('utf8',"\x{2122}");

    my $blob=Encode::encode('utf8',$text);
    $blob=~s/$retm/(TM)/sg;
    my $ntext = Encode::decode('utf8',$blob);

    ### print ".... |$text| => |$ntext|\n";

    return $ntext;
}

root@bbe78e26dc1f:~/rsh# perl memtest-u2a.pl 

INITIAL: 9900
---------------- CYCLE: 9, since-last 136, total 136, initial 9900, current 10036
---------------- CYCLE: 22, since-last 132, total 260, initial 9900, current 10160
---------------- CYCLE: 34, since-last 132, total 392, initial 9900, current 10292
---------------- CYCLE: 46, since-last 132, total 516, initial 9900, current 10416
---------------- CYCLE: 58, since-last 136, total 644, initial 9900, current 10544
---------------- CYCLE: 71, since-last 136, total 772, initial 9900, current 10672
---------------- CYCLE: 83, since-last 132, total 896, initial 9900, current 10796
---------------- CYCLE: 95, since-last 132, total 1020, initial 9900, current 10920
---------------- CYCLE: 108, since-last 136, total 1156, initial 9900, current 11056
---------------- CYCLE: 120, since-last 136, total 1284, initial 9900, current 11184
---------------- CYCLE: 132, since-last 132, total 1408, initial 9900, current 11308
---------------- CYCLE: 145, since-last 132, total 1532, initial 9900, current 11432
---------------- CYCLE: 157, since-last 136, total 1668, initial 9900, current 11568
---------------- CYCLE: 170, since-last 136, total 1796, initial 9900, current 11696
---------------- CYCLE: 182, since-last 132, total 1920, initial 9900, current 11820
---------------- CYCLE: 194, since-last 136, total 2048, initial 9900, current 11948
FINAL: 11940, LEAKED 2040

root@bbe78e26dc1f:~/rsh# perl -v

This is perl 5, version 30, subversion 0 (v5.30.0) built for x86_64-linux-gnu

Copyright 1987-2019, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on
this system using "man perl" or "perldoc perl".  If you have access to the
Internet, point your browser at http://www.perl.org/, the Perl Home Page.