doc: clarify in texinfo that `test == ...` is non portable

* doc/coreutils.texi (test invocation): Mention non portability
of the double equals form.

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 8d9320ca248b6e9bcfc9f1b0fda15da0de6361ec..99f6d9fb8b40875fe8a957de03821a899563a86c 100644 (file)
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -13336,6 +13336,8 @@ True if the strings are equal.
 @opindex ==
 @cindex equal string check
 True if the strings are equal (synonym for =).
+Note this form is not as portable to other
+shells and systems.
 
 @item @var{string1} != @var{string2}
 @opindex !=