How can a zsh script test whether it is being sourced?

Question

The accepted answer for a similar question for bash does not seem to work for zsh. In fact, if I copy basically the same code given in that answer, to produce the script

#!/usr/bin/zsh -
# test.sh

[[ $_ != $0 ]] && echo "sourced\n" || echo "subshell\n"

the output hardly ever corresponds to the actual situation:

zsh% chmod +x ./test.sh
zsh% env -i /usr/bin/zsh -f
zsh% ./test.sh
sourced

zsh% /usr/bin/zsh ./test.sh
sourced

zsh% /bin/bash ./test.sh
sourced

zsh% source ./test.sh
subshell

zsh% . ./test.sh
subshell

zsh% env -i /bin/bash --norc --noprofile
bash-3.2$ ./test.sh
sourced

bash-3.2$ /usr/bin/zsh ./test.sh
sourced

bash-3.2$ /bin/bash ./test.sh
sourced

bash-3.2$ source ./test.sh
sourced

bash-3.2$ . ./test.sh
sourced

When the current interactive shell is zsh, the script gets it exactly wrong every time. It fares a bit better under bash (though in a way reminiscent of the stopped watch that gets the time exactly right twice a day).

These truly abysmal results give me little confidence in this approach.

Is there something better?

Answer 1

if [[ $ZSH_EVAL_CONTEXT == 'toplevel' ]]; then
    # We're not being sourced so run the colors command which in turn sources
    # this script and uses its content to produce representative output.
    colors
fi

Via Kurtis Rader on the zsh-users mailing list.

Answer 2

To see if the code is running in a subshell, check the value of $ZSH_SUBSHELL:

if (( ZSH_SUBSHELL )); then
  echo "subshell, $ZSH_SUBSHELL fork(s) deep"
else
  echo "not a subshell"
fi

• $ZSH_SUBSHELL evaluates to 0 if , and only if, you’re not in a subshell. See http://zsh.sourceforge.net/Doc/Release/Parameters.html#Parameters-Set-By-The-Shell

To see if the code is sourced, check if zsh_eval_context contains the word file:

if (( zsh_eval_context[(I)file] )); then
  echo "sourced"
else
  echo "not sourced"
fi

• $zsh_eval_context will contain the word file when the code is being read directly from a file, such as when using the . or source builtins. See http://zsh.sourceforge.net/Doc/Release/Parameters.html#Parameters-Set-By-The-Shell
• $zsh_eval_context[(I)file] evaluates to 0 if $zsh_eval_context does not contain the word file. See https://zsh.sourceforge.io/Doc/Release/Parameters.html#Array-Subscripts

Answer 3

You could get the Shell Level:

[ $SHLVL -gt 1 ] && echo "subshell"

There's also (ZSH-only) $ZSH_SUBSHELL.

Obviously these break if you're nesting.

Answer 4

Isn't the answer you are looking for the difference between login and interactive shell?

localhost% cat foo
#!/usr/bin/env zsh

[[ $- == *i* ]] && print ' interactive=sourced' || print ' login=called'

localhost% source foo
 interactive=sourced
localhost% zsh foo   
 login=called