doc: join: clarify that -e only effective for -12jo fields

* src/join.c (usage): Clarify that -e is not sufficient
to enable output of missing fields from one of the inputs.
Rather the -12jo options are required to explicitly
enable output of those fields.
Fixes https://bugs.gnu.org/54625

diff --git a/src/join.c b/src/join.c
index 3d62ca43a359aefe88ba96c55f7f07d6fd8a0166..f2fd1727b3f3945c12a70f4a2bf648349f0f9c86 100644 (file)
--- a/src/join.c
+++ b/src/join.c
@@ -206,7 +206,11 @@ When FILE1 or FILE2 (not both) is -, read standard input.\n\
 \n\
   -a FILENUM             also print unpairable lines from file FILENUM, where\n\
                            FILENUM is 1 or 2, corresponding to FILE1 or FILE2\n\
-  -e EMPTY               replace missing input fields with EMPTY\n\
+"), stdout);
+      fputs (_("\
+  -e STRING              replace missing (empty) input fields with STRING;\n\
+                           I.e., missing fields specified with '-12jo' options\
+\n\
 "), stdout);
       fputs (_("\
   -i, --ignore-case      ignore differences in case when comparing fields\n\