I'm not sure exactly how you wanted your script to work, but here's my attempt at a more structured version of your code.

Take notice that I've use 'eq' instead of '=' when comparing the values. '=' is the assignment operator, it doesn't compare two strings. Don't feel bad though, it's one of the biggest gotchas, and _everybody_ has done it at some point.

You also need to chomp the value from STDIN, as this will always have a new line ('\n') char at the end, and comparing $string eq "whatever" won't work because of the extra character

print("Type R to re-enter the values or Type E to exit:\n");
my @values;
while (<STDIN>) {

    my $value = $_;
    chomp($value);

    last if $value eq 'E';
    
    if ($value eq 'R') {
        @values = ();
        print "values have been cleared\n";
    } else {
        push(@values, $value);
    }
}

print join(',', @values) . "\n";
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