Support extproc on OS/2

extproc is similar to like #! on OS/2.

exec.c

@@ -930,9 +930,12 @@ scriptexec(struct op *tp, const char **ap)
 		cp = buf + n;
 		/* bail out if no shebang magic found */
 		if ((cp[0] != '#') || (cp[1] != '!'))
+#ifdef __OS2__
+			if (strncmp(cp, "extproc", 7) || (cp[7] != ' ' && cp[7] != '\t'))
+#endif
 			goto noshebang;
 
-		cp += 2;
+		cp += *cp == '#' ? 2 : 7;
 		/* skip whitespace before shell name */
 		while (*cp == ' ' || *cp == '\t')
 			++cp;

funcs.c

@@ -160,6 +160,9 @@ const struct builtin mkshbuiltins[] = {
 #ifdef __MirBSD__
 	/* alias to "true" for historical reasons */
 	{"domainname", c_true},
+#endif
+#ifdef __OS2__
+	{"extproc", c_true},
 #endif
 	{NULL, (int (*)(const char **))NULL}
 };

main.c

@@ -454,7 +454,18 @@ main_init(int argc, const char *argv[], Source **sp, struct block **lp)
 			kshname = argv[argi++];
 	} else if (argi < argc && !Flag(FSTDIN)) {
 		s = pushs(SFILE, ATEMP);
+#ifndef __OS2__
 		s->file = argv[argi++];
+#else
+		/* a bug in os2 extproc shell processing doesn't pass full pathname
+		 * of a script so we have to search for it.
+		 * This changes the behavior of 'ksh arg' to search the users search
+		 * path but it can't be helped.
+		 */
+		s->file = search_path(argv[argi++], path, X_OK, NULL);
+		if (!s->file || !*s->file)
+			s->file = argv[argi - 1];
+#endif
 		s->u.shf = shf_open(s->file, O_RDONLY, 0,
 		    SHF_MAPHI | SHF_CLEXEC);
 		if (s->u.shf == NULL) {