How can I test if a script was invoked using `. script.sh` vs `bash script.sh`?

Question

I'm writing a script as part of a process to restore a broken environment. It sources a couple of other scripts, and I want all of those variables to be maintained on the command line after running the script. For this reason, the script needs to be run using . script.sh and not using bash script.sh.

I want to add a line or two in the script to make sure that the user has invoked the script correctly, and not used bash script.sh, as this will cause problems further along in the process.

How can I test whether or not the script was invoked using . script.sh (or at least that the sourced commands will persist after the script has completed)?

Answer 1

If you want to distinguish between . script.sh and bash script.sh (or doing a chmod 755 and a ./script.sh or PATH=. script.sh) while preserving the ability to do . foo/script.sh or some such thing, do this:

if [[ $0 = *bash ]]; then
  echo "Invoked using source (.)"
else
  echo "Invoked as executable"
fi

$0 will either contain -bash or bash for a sourced script, or the name of the file for an executed script.

Let me show you the effect:

$ cat test.sh
foo=$((foo+1))
if [[ $0 = *bash ]]; then
  echo "Invoked using source (.)"
else
  echo "Invoked as executable"
fi
$ foo=0
$ . test.sh; echo $foo
Invoked using source (.)
1
$ source test.sh; echo $foo
Invoked using source (.)
2
$ . ./test.sh; echo $foo
Invoked using source (.)
3
$ bash test.sh; echo $foo
Invoked as executable
3
$ ./test.sh; echo $foo
Invoked as executable
3
$ PATH=. test.sh; echo $foo
Invoked as executable
3
$ bash
$ echo $foo

$ . test.sh; echo $foo
Invoked using source (.)
1
$ ./test.sh; echo $foo
Invoked as executable
1

Answer 2

@stéphane-chazelas provided the answer in a comment. Thank you.

if [[ $BASH_SOURCE = ./test.sh ]]; then
    echo "using ./test.sh"
else
    echo "using bash test.sh (or similar)"
fi