sh: Prefer "" to nullstr where possible.

bin/sh/cd.c

@@ -122,7 +122,7 @@ cdcmd(int argc __unused, char **argv __unused)
 	    (dest[0] == '.' && (dest[1] == '/' || dest[1] == '\0')) ||
 	    (dest[0] == '.' && dest[1] == '.' && (dest[2] == '/' || dest[2] == '\0')) ||
 	    (path = bltinlookup("CDPATH", 1)) == NULL)
-		path = nullstr;
+		path = "";
 	while ((p = padvance(&path, dest)) != NULL) {
 		if (stat(p, &statb) < 0) {
 			if (errno != ENOENT)

bin/sh/eval.c

@@ -498,7 +498,7 @@ exphere(union node *redir, struct arglist *fn)
 	struct localvar *savelocalvars;
 	int need_longjmp = 0;
 
-	redir->nhere.expdoc = nullstr;
+	redir->nhere.expdoc = "";
 	savelocalvars = localvars;
 	localvars = NULL;
 	forcelocal++;

bin/sh/expand.c

@@ -530,8 +530,7 @@ subevalvar(char *p, char *str, int strloc, int subtype, int startloc,
 			error((char *)NULL);
 		}
 		error("%.*s: parameter %snot set", (int)(p - str - 1),
-		      str, (varflags & VSNUL) ? "null or "
-					      : nullstr);
+		      str, (varflags & VSNUL) ? "null or " : "");
 		return 0;
 
 	case VSTRIMLEFT:

bin/sh/mail.c

@@ -85,7 +85,7 @@ chkmail(int silent)
 	setstackmark(&smark);
 	mpath = mpathset()? mpathval() : mailval();
 	for (i = 0 ; i < nmboxes ; i++) {
-		p = padvance(&mpath, nullstr);
+		p = padvance(&mpath, "");
 		if (p == NULL)
 			break;
 		if (*p == '\0')

bin/sh/miscbltin.c

@@ -265,7 +265,7 @@ readcmd(int argc __unused, char **argv __unused)
 
 	/* Set any remaining args to "" */
 	while (*++ap != NULL)
-		setvar(*ap, nullstr, 0);
+		setvar(*ap, "", 0);
 	return status;
 }
 

bin/sh/nodetypes

@@ -138,7 +138,7 @@ NXHERE nhere			# fd<<!
 	fd	  int			# file descriptor being redirected
 	next	  nodeptr		# next redirection in list
 	doc	  nodeptr		# input to command (NARG node)
-	expdoc    temp	char *expdoc	# actual document (for NXHERE)
+	expdoc    temp	const char *expdoc	# actual document (for NXHERE)
 
 NNOT nnot			# ! command  (actually pipeline)
 	type	int

bin/sh/parser.c

@@ -1940,7 +1940,7 @@ getprompt(void *unused __unused)
 	 */
 	switch (whichprompt) {
 	case 0:
-		fmt = nullstr;
+		fmt = "";
 		break;
 	case 1:
 		fmt = ps1val();

bin/sh/var.c

@@ -872,7 +872,7 @@ unsetvar(const char *s)
 	if (vp->flags & VREADONLY)
 		return (1);
 	if (vp->text[vp->name_len + 1] != '\0')
-		setvar(s, nullstr, 0);
+		setvar(s, "", 0);
 	if ((vp->flags & VEXPORT) && localevar(vp->text)) {
 		change_env(s, 0);
 		setlocale(LC_ALL, "");