Remove the underscore prefix of __bp_imported (#123)

* Remove the underscore prefix of "__bp_imported"

This formally exposes it as part of the public API.

* Fix Bats test after renaming the variable

* Rename the variable upon reviewer request

* Fix inconsistency after renaming variables

Variables were reanmed in 7fbc07fb4e, but
it didn’t cover the test or ReadMe. This commit fixes that.

README.md

@@ -91,6 +91,15 @@ export __bp_enable_subshells="true"
 ```
 This is disabled by default due to buggy situations related to to `functrace` and Bash's `DEBUG trap`. See [Issue #25](https://github.com/rcaloras/bash-preexec/issues/25)
 
+## Library authors
+If you want to detect bash-preexec in your library (for example, to add hooks to `preexec_functions` when available), use the Bash variable `bash_preexec_imported`:
+
+```bash
+if [[ -n "${bash_preexec_imported:-}" ]]; then
+    echo "Bash-preexec is loaded."
+fi
+```
+
 ## Tests
 You can run tests using [Bats](https://github.com/bats-core/bats-core).
 ```bash

bash-preexec.sh

@@ -38,10 +38,14 @@ if [[ -z "${BASH_VERSION:-}" ]]; then
 fi
 
 # Avoid duplicate inclusion
-if [[ "${__bp_imported:-}" == "defined" ]]; then
+if [[ -n "${bash_preexec_imported:-}" ]]; then
     return 0
 fi
-__bp_imported="defined"
+bash_preexec_imported="defined"
+
+# WARNING: This variable is no longer used and should not be relied upon.
+# Use ${bash_preexec_imported} instead.
+__bp_imported="${bash_preexec_imported}"
 
 # Should be available to each precmd and preexec
 # functions, should they want it. $? and $_ are available as $? and $_, but

test/include-test.bats

@@ -1,13 +1,13 @@
 #!/usr/bin/env bats
 
 @test "should not import if it's already defined" {
-  __bp_imported="defined"
+  bash_preexec_imported="defined"
   source "${BATS_TEST_DIRNAME}/../bash-preexec.sh"
   [ -z $(type -t __bp_install) ]
 }
 
 @test "should import if not defined" {
-  unset __bp_imported
+  unset bash_preexec_imported
   source "${BATS_TEST_DIRNAME}/../bash-preexec.sh"
   [ -n $(type -t __bp_install) ]
 }