Implement $SHELL and $0 (How to identify which shell I am in)

[certik]

The shell now looks identical to Bash! How can I tell which shell I am in? This morning I started in our shell, and I only noticed when git tab completion didn't work (#80) that I am not in Bash.

[certik]

Some ideas:

• maybe some command to run "which_shell_am_I" (but shorter)
• some key binding (Ctrl-H or F1) for a nice help / about screen
• maybe make the shell look different (but I like that it looks like Bash)

[awvwgk]

For shells like Bash or Zsh the shell running is always exported in the SHELL environment variable.

[certik]

@awvwgk great idea! Indeed, $SHELL works, so we should just implement it and that will fix this for me.

[certik]

Apparently there is also $0:

$ echo $0
-bash

[gxyd]

For shells like Bash or Zsh the shell running is always exported in the SHELL environment variable.

I think there is a difference between $SHELL and $0, as provided here:

https://stackoverflow.com/questions/9804517/difference-between-0-and-shell#:~:text=%24SHELL%20gives%20the%20full%20path,name%20of%20your%20current%20shell.

[certik]

I see. The $SHELL environment variable is a shell that the user wants to be using for future shell invocations from various programs. That's a separate feature.

The main feature I want in this issue is to determine which shell I am running right now, and for that we need to implement $0 which will print the currently running program (shell).

[certik]

To fix this issue: implement echo $0, it needs to show the absolute path to the shell. Currently it is empty.

[wolfv]

I implemented something in #232 (also implements printenv)

[wolfv]

I implemented something but I think it doesn't hit the mark yet.

This is my test script:

echo $0
echo "Args: $1 $2 $3"
echo $#
echo $@

Note that shell is defined on a different level and supposed to stay constant. You can define $SHELL in one of your profile files to the shell that you like as default (similar to $EDITOR).

[wolfv]

Also, when you run bash ./script.sh, then $0 will not print the path to the shell, but the path to script.sh. You would have to inspect the parent process.

I think we could implement $SHELL_VERSION similar to BASH_VERSION / ZSH_VERSION as a simple method. Everything else requires some fiddling with parent process lookup.