How to get shell to self-detect using zsh or bash

Question

I've a question on how to tell which shell the user is using. Suppose a script that if the user is using zsh, then put PATH to his .zshrc and if using bash should put in .bashrc. And set rvmrc accordingly.

#!/usr/bin/env bash
export PATH='/usr/local/bin:$PATH' >> ~/.zshrc
source ~/.zshrc

I've tried the following but it does not work : (

if [[ $0 == "bash" ]]; then
  export PATH='/usr/local/bin:$PATH' >> ~/.bashrc
elif [[ $0 == "zsh" ]]; then
  export PATH='/usr/local/bin:$PATH' >> ~/.zshrc
fi

# ... more commands ...

if [[ $0 == "bash" ]]; then
  [[ -s '/Users/`whoami`/.rvm/scripts/rvm' ]] && source '/Users/`whoami`/.rvm/scripts/rvm' >> ~/.bashrc
  source ~/.bashrc
elif [[ $0 == "zsh" ]]; then
  [[ -s '/Users/`whoami`/.rvm/scripts/rvm' ]] && source '/Users/`whoami`/.rvm/scripts/rvm' >> ~/.zshrc
  source ~/.zshrc
fi

Answer 1

If the shell is Zsh, the variable $ZSH_VERSION is defined. Likewise for Bash and $BASH_VERSION.

if [ -n "$ZSH_VERSION" ]; then
   # assume Zsh
elif [ -n "$BASH_VERSION" ]; then
   # assume Bash
else
   # assume something else
fi

However, these variables only tell you which shell is being used to run the above code. So you would have to source this fragment in the user's shell.

As an alternative, you could use the $SHELL environment variable (which should contain absolute path to the user's preferred shell) and guess the shell from the value of that variable:

case $SHELL in
*/zsh) 
   # assume Zsh
   ;;
*/bash)
   # assume Bash
   ;;
*)
   # assume something else
esac

Of course the above will fail when /bin/sh is a symlink to /bin/bash.

If you want to rely on $SHELL, it is safer to actually execute some code:

if [ -n "`$SHELL -c 'echo $ZSH_VERSION'`" ]; then
   # assume Zsh
elif [ -n "`$SHELL -c 'echo $BASH_VERSION'`" ]; then
   # assume Bash
else
   # assume something else
fi

This last suggestion can be run from a script regardless of which shell is used to run the script.