Junio Hamano, junio at twinsun dot com writes:

The sed command in busybox 1.0.0-pre8 loses leading whitespace
in 'a' command ('i' and 'c' commands are also affected).  A
patch to fix this is attached at the end of this message.

The following is a transcript that reproduces the problem.  The
first run uses busybox 1.0.0-pre3 as "/bin/sed" command, which
gets the expected result.  Later in the test, /bin/sed symlink
is changed to point at busybox 1.0.0-pre8 and the test script is
run again, which shows the failure.

=== reproduction recipe ===
* Part 1.  Use busybox 1.0.0-pre3 as sed; this works.

root# cd /tmp
root# cat 1.sh
#!/bin/sh

cd /tmp
rm -f ipsec.conf ipsec.conf+
cat >ipsec.conf <<\EOF
version 2.0

config setup
        klipsdebug=none
        plutodebug=none
        plutostderrlog=/dev/null

conn %default
        keyingtries=1
        ...
EOF
sed -e '/^config setup/a\
	nat_traversal=yes' ipsec.conf >ipsec.conf+
mv -f ipsec.conf+ ipsec.conf
root# sh -x 1.sh
+ cd /tmp
+ rm -f ipsec.conf ipsec.conf+
+ cat
+ sed -e /^config setup/a\
        nat_traversal=yes ipsec.conf
+ mv -f ipsec.conf+ ipsec.conf
root# cat ipsec.conf
version 2.0

config setup
        nat_traversal=yes
        klipsdebug=none
        plutodebug=none
        plutostderrlog=/dev/null

conn %default
        keyingtries=1
        ...
root# sed --version
sed: invalid option -- -
BusyBox v1.00-pre3 (2004.02.26-18:47+0000) multi-call binary

Usage: sed [-nef] pattern [files...]

* Part 2.  Continuing from the above, use busybox 1.0.0-pre8
  as sed; this fails.

root# ln -s busybox-pre8 /bin/sed-8
root# mv /bin/sed-8 /bin/sed
root# sed --version
This is not GNU sed version 4.0
root# sed --
BusyBox v1.00-pre8 (2004.03.30-02:44+0000) multi-call binary

Usage: sed [-nef] pattern [files...]
root# sh -x 1.sh
+ cd /tmp
+ rm -f ipsec.conf ipsec.conf+
+ cat
+ sed -e /^config setup/a\
        nat_traversal=yes ipsec.conf
+ mv -f ipsec.conf+ ipsec.conf
root# cat ipsec.conf
version 2.0

config setup
nat_traversal=yes
        klipsdebug=none
        plutodebug=none
        plutostderrlog=/dev/null

conn %default
        keyingtries=1
        ...
root#
=== reproduction recipe ends here ===

This problem was introduced in 1.0.0-pre4.  The problem is that
the command argument parsing code strips leading whitespaces too
aggressively.  When running the above example, the piece of code
in question gets "\n\tnat_traversal=yes" as its argument in
cmdstr variable (shown part in the following patch).  What it
needs to do at this point is to strip the first newline and
nothing else, but it instead strips all the leading whitespaces
at the beginning of the string, thus losing the tab character.
The following patch fixes this.

editors/sed.c

@@ -410,7 +410,9 @@ static char *parse_cmd_args(sed_cmd_t *sed_cmd, char *cmdstr)
 		if ((sed_cmd->end_line || sed_cmd->end_match) && sed_cmd->cmd != 'c')
 			bb_error_msg_and_die
 				("only a beginning address can be specified for edit commands");
-		while(isspace(*cmdstr)) cmdstr++;
+		if (*cmdstr != '\n') /* should not happen */
+		  bb_error_msg_and_die("A/I/C backslash not followed by NL?");
+		cmdstr++; /* skip over the NL following the backslash */
 		sed_cmd->string = bb_xstrdup(cmdstr);
 		parse_escapes(sed_cmd->string,sed_cmd->string,strlen(cmdstr),0,0);
 		cmdstr += strlen(cmdstr);