run-command: optimize out useless shell calls

If there are no metacharacters in the program to be run, we
can just skip running the shell entirely and directly exec
the program.

The metacharacter test is pulled verbatim from
launch_editor, which already implements this optimization.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

run-command.c

@@ -28,15 +28,17 @@ static const char **prepare_shell_cmd(const char **argv)
 	if (argc < 1)
 		die("BUG: shell command is empty");
 
-	nargv[nargc++] = "sh";
-	nargv[nargc++] = "-c";
-
-	if (argc < 2)
-		nargv[nargc++] = argv[0];
-	else {
-		struct strbuf arg0 = STRBUF_INIT;
-		strbuf_addf(&arg0, "%s \"$@\"", argv[0]);
-		nargv[nargc++] = strbuf_detach(&arg0, NULL);
+	if (strcspn(argv[0], "|&;<>()$`\\\"' \t\n*?[#~=%") != strlen(argv[0])) {
+		nargv[nargc++] = "sh";
+		nargv[nargc++] = "-c";
+
+		if (argc < 2)
+			nargv[nargc++] = argv[0];
+		else {
+			struct strbuf arg0 = STRBUF_INIT;
+			strbuf_addf(&arg0, "%s \"$@\"", argv[0]);
+			nargv[nargc++] = strbuf_detach(&arg0, NULL);
+		}
 	}
 
 	for (argc = 0; argv[argc]; argc++)