use Perl

#!/Users/colomon/tools/rakudo/perl6
my $search_word = @*ARGS.shift;
my $replacement = @*ARGS.shift;

sub UpperCaseEachWord($word)
{
    my @words = $word.split('_');
    my @uppered = map {$_.lc.ucfirst}, @words;
    return @uppered.join('');
}

my %substitutions;
%substitutions{$search_word.lc} = $replacement.lc;
%substitutions{$search_word.uc} = $replacement.uc;
%substitutions{UpperCaseEachWord($search_word)} = UpperCaseEachWord($replacement);

# for %substitutions.pairs -> $x
# {
#     say "{$x.key}, {$x.value}";
# }

for =$*IN -> $text is rw
{
    for %substitutions.pairs -> $sub
    {
        $text .= subst($sub.key, $sub.value, :g);
    }
    say $text;
}