Fish interpreter fails to execute code snippets with command substitution error: `command substitutions not allowed in command position. Try var=(your-cmd) $var ... __cleanup() {`

[suin]

Description

When specifying fish as the interpreter for a code snippet in Runme, the execution fails with a command substitution error. The same code snippet works correctly when using bash as the interpreter.

Environment

• Runme version: 3.14.0
• Fish version: 4.0.2
• Bash version: 5.2.37

Steps to Reproduce

1. Create a README.md file with a fish code block:

   ```fish {"interpreter":"fish","name":"fish-test"}
   echo "Hello, World!"
   ```

2. Run the snippet using runme:

   runme run fish-test

Expected Behavior

The snippet should execute successfully and output:

Hello, World!

Actual Behavior

The execution fails with the following error:

/tmp/runme/.runme-script-01JYD6NM79ARD8D9CYNNX3T5JH.sh (line 2): command substitutions not allowed in command position. Try var=(your-cmd) $var ...
__cleanup() {
         ^^
warning: Error while reading file /tmp/runme/.runme-script-01JYD6NM79ARD8D9CYNNX3T5JH.sh
could not execute command: failed to run command "fish-test": exit code: 127

Additional Context

The same code snippet works correctly when using bash as the interpreter:

```bash {"interpreter":"bash","name":"bash-test"}
echo "Hello, World!"
```

Running runme run bash-test produces the expected output:

Hello, World!

Possible Cause

It appears that Runme might be generating a shell script with bash-specific syntax (such as the __cleanup() function definition) that is incompatible with fish shell's syntax. Fish has a different syntax for function definitions and doesn't support the same command substitution syntax as bash.

Suggested Solution

When using fish as an interpreter, Runme should either:

1. Generate fish-compatible wrapper scripts, or
2. Use a different approach that doesn't rely on bash-specific syntax in the wrapper script

Related Information

• Fish shell documentation on [function syntax](https://fishshell.com/docs/current/language.html#syntax-function)
• Fish shell [differences from bash](https://fishshell.com/docs/current/fish_for_bash_users.html)