doc: Document how to deal with missing 'join'.

* doc/autoconf.texi (Limitations of Usual Tools): Mention that 'join' is missing
in BusyBox.

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 04730dcc3c942d100b42189d325292038e412b30..06a98dd0b808192d533583f79df26a87ebcaafe6 100644 (file)
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -19624,6 +19624,12 @@ On NetBSD, @command{join -a 1 file1 file2} mistakenly behaves like
 @command{join -a 1 -a 2 1 file1 file2}, resulting in a usage warning;
 the workaround is to use @command{join -a1 file1 file2} instead.
 
+On platforms with the BusyBox tools, the @command{join} command is
+entirely missing.  As a workaround, you can simulate special cases of the
+@command{join} command using an @command{awk} script.  For an example,
+see @url{https://lists.gnu.org/r/bug-gnulib/2021-04/msg00054.html}.
+
+
 @item @command{ln}
 @c ---------------
 @prindex @command{ln}