><>, 9 8 bytes

Thanks to Sp3000 for saving a byte.

'i$-%n
/

There's an unprintable 0x01 before the /.

Try it online!

Explanation

This is a port of my character code-based Labyrinth answer.

'     Push the entire program (except ' itself) onto the stack, which ends 
      with [... 1 47].
i     Read the first character of the input.
$-    Subtract the 47.
%     Take the 1 modulo this value.
n     Output the result as an integer.
0x01  Unknown command, terminates the program.

><>, 9 8 bytes

Thanks to Sp3000 for saving a byte.

'i$-%n
/

There's an unprintable 0x01 before the /.

Try it online!

Explanation

This is a port of my character code-based Labyrinth answer.

'     Push the entire program (except ' itself) onto the stack, which ends 
      with [... 1 47].
i     Read the first character of the input.
$-    Subtract the 47.
%     Take the 1 modulo this value.
n     Output the result as an integer.
0x01  Unknown command, terminates the program.

><>, 9 bytes

1i"/"-%n;

Try it online!

A port of my character code-based Labyrinth answer.

><>, 9 8 bytes

Thanks to Sp3000 for saving a byte.

'i$-%n
/

There's an unprintable 0x01 before the /.

Try it online!

Explanation

This is a port of my character code-based Labyrinth answer.

'     Push the entire program (except ' itself) onto the stack, which ends 
      with [... 1 47].
i     Read the first character of the input.
$-    Subtract the 47.
%     Take the 1 modulo this value.
n     Output the result as an integer.
0x01  Unknown command, terminates the program.