Start a subshell

In a Bash shell, you can invoke another Bash subshell in interactive mode.

$ bash

You might not see anything different in the prompt. Though some variables from the outer shell won’t be available. Any variables you set in the inner shell won’t be available in the outer shell. Also your Python environment could no longer be active.

If you enter exit or press CTRL+D, then you will return to the outer shell session.

Note that you should not use this to switch between shells, as the config file will not be executed appropriately. Use the Start new shell session section below.

Get current shell

This will print the program name, which in the case of the shell is the actual shell. source

Conditional

In short, the most reliable way in conditional flow is this. To be tested. Perhaps it can work with case.

IS_BASH=false
IS_ZSH=false

if [[ "$0" == *bash* ]]; then
  IS_BASH=true
else if [[ "$0" == *zsh* ]];
  IS_ZSH=true
fi

# OR - more lines but DRY.

case "$0)" in
  *bash* )
    IS_BASH=true
    ;;
  *zsh* )
    IS_LINUX=true
    ;;
esac

Note:

If using a single boolean:

$ IS_ZSH=$([[ "$ZSH_NAME" ]] && echo 'true' || echo 'false')

Using $0

Tested on macOS

  • Bash 
      $ echo $0
  -bash
  # Or
  • ZSH 
      $ echo $0
  -zsh

Tested on Linux

$ # In terminal.
$ echo $0
/bin/bash

$ # In subshell.
$ bash -c 'echo $0'
bash

ZSH - to be checked.

Using BASH or ZSH_NAME variables

  • Bash 
      $ echo $BASH
  # ?
    • This is only set when using Bash. However, this weirdly gave response as /bin/zsh when using Bash when ZSH was the default shell, so need to investigate this further.
  • ZSH 
      $ echo $ZSH_NAME
  zsh

Using SHELL

This shows the default shell, not your current shell.

$ echo $SHELL

source

Change shell

Start new shell session

Replace the current terminal session with a new one. Use the exec command with the –login flag so the shell acts as if invoked by login. source

$ exec -l zsh

$ exec -l bash

Change default shell

To change to ZSH, run one of:

$ chsh -s /bin/zsh

$ chsh -s $(which zsh)

Reload shell

If you have edited your Bash configs and want to reload them, you can do this:

source ~/.bashrc
source ~/.bash_profile

Alternatives below, if you are happy to lose shell history. source

Run this. This runs the login option to ensure bash profile is loaded.

bash -l

Or completely replace the current shell. If you exit, the terminal tab will exit and you will no go to the outer shell.

exec -l bash

Create an function in your ~/.bashrc if you easily run it. This reloads the default shell, not your current shell.

reload_shell() { exec -l $SHELL; }