How to Reverse Characters in a Variable

Questions & Suggestions
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If you only have singlebyte characters in your input (for example [a-z][A-Z][0-9]) you can also get away with a very nice and short Perl solution:

39-pty-fs8

#!/usr/bin/env perl

use strict;
use warnings;

$_ =  reverse <>;
print;

Or as a command-line one-liner:

perl -pe '$_ = reverse'

‌

[Skip the rest of this post if you are not interested in reversing any kind of UTF characters.]

The pitfall (or: “what I have learned today :wink: ) is that this fails to a different degree if the string contains multibyte UTF characters like ä, é, ợ, đ etc.

For the more simple things like Käse, résumé etc. it seems to be sufficient to explicitly set the stdin mode to “utf8” with

binmode STDIN, ':utf8';

With this modification, the Perl script from above produces correctly esäK and émusér.

But with more “sophisticated” strings like Rượu đế this is not enough.

So far the only solutions I have found to work with any kind of strings are these:

1) — Splitting the string with the \X special (“Match Unicode eXtended grapheme cluster”):

#!/usr/bin/env perl

use strict;
use warnings;

binmode STDIN, ':utf8';

$_ = join('', reverse <> =~ /\X/g);
print;

From perldoc.perl.org

2) — Or using the Unicode::GCString module and reversing the result as list:

#!/usr/bin/env perl

use strict;
use warnings;
use Unicode::GCString;

binmode STDIN, ':utf8';

my $str = Unicode::GCString->new(<>);
$_ = join '', reverse @{ $str->as_arrayref };
print;

From Stack Overflow

As test case I have used the nice Vietnamese word Rượu đế, found in a related discussion on perlmonks.org.

The correct reverse string is ếđ uợưR.

Depending on the used technique, I’ve seen two different wrong results:

  • Ì‚Ìe‘Ä u£Ì›Ìo›ÌuR when using the multibyte incompatible script at the top of this post, and
  • ́̂eđ ựơuR when only setting the binmode to utf8.

If you want to try the scripts above:

All the scripts are written to be used in a KM Shell Script action with input from a variable (stdin), as shown in the screenshot at the top.
You should also set the output to a (non-local) variable, because the KM Shell Script Results window doesn’t show all characters correctly. (At least on my computer.)

Edit/PS:

If you want to test a script with the Vietnamese test string, you have to copy it from the following line (do not copy one of the inline instances in the text!) :

Rượu đế

Although the string looks different here, this will maintain the original composition of the characters. Once you paste the string into a Unicode-compliant editor (and using a compliant font) on your computer it will again look like “ Rượu đế ”, but with the correct composition.

Alternatively you can copy the string from inside this macro.

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