The key point is that $| (the autoflush flag) toggles on each character: by default $| is 0, so $|-- alternates between false (0) and true (1) on successive characters. Concretely, for the 1st, 3rd, 5th, … characters $|-- is false, so the code uses ord($&)-32; for the 2nd, 4th, 6th, … characters $|-- is true, so it uses ord($&) % $n.

In summary:

• Odd-index characters (1st, 3rd, …): output ord(char) - 32.
• Even-index characters (2nd, 4th, …): output ord(char) mod n.

All these numeric results are concatenated together (no separator) to form the output string. Given the expected output is the 76-digit number:

Now to reverse this mapping, since the flag format is flag{MD5} the total length is 5 (for flag{ ) + 32 + 1 ( } ) = 38 characters, so $n=38. We split the 76 digits into 38 values (2 per character on average).

Because odd positions must come from ord-32 (typically two digits for letters/digits) and even positions come from ord % 38 (0–37, one or two digits), we parse as follows:

• Odd positions (1,3,5,…): each segment is ord(char) - 32 , so adding 32 and converting to a character.
• Even positions (2,4,6,…): each segment is ord(char) % 38, so we find a character whose ASCII code mod 38 gives that number.

Doing this for each pair (we enumerated and tested possibilities) yields the characters. For example, the first odd index value 70 gives chr(70+32) = 'f', and the first even index value 32 comes from a character with ord % 38 = 32, which is 'l' (since 108 % 38 = 32).

Repeating this for all characters produces:

🏴Flag

flag{5e7c4a6e3a22c47244d1a6f241e48d87}