Support shebang lines with amended environment

For bug#64939.

* lisp/files.el (auto-mode-interpreter-regexp): Account for possible
VARIABLE=[VALUE] operands.
* test/lisp/files-tests.el (files-tests-auto-mode-interpreter):
Add an example from the coreutils manual.

2 files changed, 7 insertions, 2 deletions

diff --git a/lisp/files.el b/lisp/files.el
index 5098d49048e..524385edc84 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -3274,12 +3274,15 @@ and `inhibit-local-variables-suffixes'.  If
     ;; Optional group 1: env(1) invocation.
     "\\("
     "[^ \t\n]*/bin/env[ \t]*"
-    ;; Within group 1: possible -S/--split-string.
+    ;; Within group 1: possible -S/--split-string and environment
+    ;; adjustments.
     "\\(?:"
     ;; -S/--split-string
     "\\(?:-[0a-z]*S[ \t]*\\|--split-string=\\)"
     ;; More env arguments.
     "\\(?:-[^ \t\n]+[ \t]+\\)*"
+    ;; Interpreter environment modifications.
+    "\\(?:[^ \t\n]+=[^ \t\n]*[ \t]+\\)*"
     "\\)?"
     "\\)?"
     ;; Group 2: interpreter.
diff --git a/test/lisp/files-tests.el b/test/lisp/files-tests.el
index 0a5c3b897e4..d4c1ef3ba67 100644
--- a/test/lisp/files-tests.el
+++ b/test/lisp/files-tests.el
@@ -1694,7 +1694,9 @@ set to."
   (files-tests--check-shebang "#!/usr/bin/env -S-vi bash -eux" 'sh-base-mode 'bash)
   (files-tests--check-shebang "#!/usr/bin/env -ivS --default-signal=INT bash -eux" 'sh-base-mode 'bash)
   (files-tests--check-shebang "#!/usr/bin/env -ivS --default-signal bash -eux" 'sh-base-mode 'bash)
-  (files-tests--check-shebang "#!/usr/bin/env -vS -uFOOBAR bash -eux" 'sh-base-mode 'bash))
+  (files-tests--check-shebang "#!/usr/bin/env -vS -uFOOBAR bash -eux" 'sh-base-mode 'bash)
+  ;; Invocation through env, with modified environment.
+  (files-tests--check-shebang "#!/usr/bin/env -S PYTHONPATH=/...:${PYTHONPATH} python" 'python-base-mode))
 
 (ert-deftest files-test-dir-locals-auto-mode-alist ()
   "Test an `auto-mode-alist' entry in `.dir-locals.el'"