Fsubstitute_in_file_name doc string clarification

* src/fileio.c (Fsubstitute_in_file_name): Mention that undefined
variables aren't replaced (as opposed to what happens in a shell
substitution) (bug#40949).

diff --git a/src/fileio.c b/src/fileio.c
index caf077e2fbf83d8dc88af197f28c6cd6a46ef127..1d9a3e1644463f2ae536aa4feaea6000950a4672 100644 (file)
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -1830,6 +1830,8 @@ the value of that variable.  The variable name should be terminated
 with a character not a letter, digit or underscore; otherwise, enclose
 the entire variable name in braces.
 
+If FOO is not defined in the environment, it is not substituted.
+
 If `/~' appears, all of FILENAME through that `/' is discarded.
 If `//' appears, everything up to and including the first of
 those `/' is discarded.  */)