Document busybox sed bug.

* doc/autoconf.texi (Limitations of Usual Tools): Mention
restrictions when using back-references.
Reported by Vincent Lefevre:
<http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/13013>.

Signed-off-by: Eric Blake <ebb9@byu.net>

diff --git a/ChangeLog b/ChangeLog
index 0aab3983f24193087b6bc1ef0a9ef2fca410c9be..7f82ee218ccfe13ba63d7495200eb1e831c5e3b1 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2008-03-26  Eric Blake  <ebb9@byu.net>
 
+       Document busybox sed bug.
+       * doc/autoconf.texi (Limitations of Usual Tools): Mention
+       restrictions when using back-references.
+       Reported by Vincent Lefevre:
+       <http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/13013>.
+
        Document Automake interaction with AC_CONFIG_MACRO_DIR.
        * doc/autoconf.texi (Input): Mention ACLOCAL_AMFLAGS for automake
        users.

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 17b90455d2a54c9b48569a72fe3a8f86b94c79ac..b72d8757b03a630b29d56b295257d94c291bafdc 100644 (file)
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -15389,6 +15389,20 @@ flushleft
    indented
 @end example
 
+Posix requires that with an empty regular expression, the last non-empty
+regular expression from either an address specification or substitution
+command is applied.  However, busybox 1.6.1 complains when using a
+substitution command with a replacement containing a back-reference to
+an empty regular expression; the workaround is repeating the regular
+expression.
+
+@example
+@kbd {echo abc | busybox sed '/a\(b\)c/ s//\1/'}
+sed: No previous regexp.
+@kbd {echo abc | busybox sed '/a\(b\)c/ s/a\(b\)c/\1/'}
+b
+@end example
+
 
 @item @command{sed} (@samp{t})
 @c ---------------------------