Can a script be used as an interpreter by the #! hashbang line?

Question

I'm trying to write a bash script which will behave as a basic interpreter, but it doesn't seem to work: The custom interpreter doesn't appear to be invoked. What am I doing wrong?

Here's a simple setup illustrating the problem:

/bin/interpreter: [owned by root; executable]

#!/bin/bash

echo "I am an interpreter running " $1

/Users/zeph/script is owned by me, and is executable:

#!/bin/interpreter

Here are some commands for the custom interpreter.

From what I understand about the mechanics of hashbangs, the script should be executable as follows:

$ ./script
I am an interpreter running ./script

But this doesn't work. Instead the following happens:

$ ./script 
./script: line 3: Here: command not found

...It appears that /bin/bash is trying to interpret the contents of ./script. What am I doing wrong?

Note: Although it appears that /bin/interpreter never invoked, I do get an error if it doesn't exist:

$ ./script
-bash: ./script: /bin/interpreter: bad interpreter: No such file or directory

(Second note: If it makes any difference, I'm doing this on MacOS X).

Answer 1

To make this work you could add the interpreter's interpreter (i.e. bash) to the shebang:

#!/bin/bash /bin/interpreter

Here are some commands for the custom interpreter.

bash will then run your interpreter with the script path in $1 as expected.

Answer 2

You can't use a script directly as a #! interpreter, but you can run the script indirectly via the env command using:

    #!/usr/bin/env /bin/interpreter

/usr/bin/env is itself a binary, so is a valid interpreter for #!; and /bin/interpreter can be anything you like (a script of any variety, or binary) without having to put knowledge of its own interpreter into the calling script.