"Hello, World!" (Robbers' thread) This is the robbers' thread. The cops' thread is here.

Your challenge is to take an uncracked submission from the cops' thread and find, for what input or inputs, the program will print Hello, World! and a newline. Capitalization, spacing, and punctuation must be exact.

Please comment on the cop's submission when you've cracked their code.
Bash by Sisyphus

Original code:

[[ ! "${1////x}" =~ [[:alnum:]] ]]&amp;&amp;[[ $# = 1 ]]&amp;&amp;bash -c "$1"


Input:

__=; (( __++, __-- ));
(( ___        = __,        ___++));
(( ____       = ___,       ____++));
(( _____      = ____,      _____++));
(( ______     = _____,     ______++));
(( _______    = ______,    _______++));
(( ________   = _______,   ________++));
(( _________  = ________,  _________++));

${!__##-} &lt;&lt;&lt;\$\'\\$___$______$_______\\$___$______$_____\\$___$_______$__\\$___$_______$_________\'\ \$\'\\$___$___$__\\$___$______$_______\\$___$_______$______\\$___$_______$______\\$___$_______$_________,\ \\$___$____$_________\\$___$_______$_________\\$___$________$____\\$___$_______$______\\$___$______$______\\$__$______$___\'


Explanation:

This encodes "echo Hello, World!" as octal escape sequences (\xxx).

Except you also can't use numbers, so the first part builds up variables for the numbers 0-7. You can use those to build a string with octal sequences that will evaluate to give you the actual command.

But eval is also alphanumeric. So instead this pipes that string as input to another instance of bash. $0 contains the name of the command used to invoke Bash, which is usually just bash (or -bash for a login shell) if you're running it normally (through TIO or by pasting it in a terminal). (This incidentally means that if you try to run this by pasting it into a script, things will go horribly wrong as it tries to fork itself a bunch of times.)

But anyway, you can't say $0 directly. Instead, $__ contains the name of $0 ("0"), and you can use indirect expansion to access it (${!__} refers to the contents of $0).

And that, finally, gives you all the pieces you need.