zn(1): proof of concept

Makefile

@@ -171,3 +171,8 @@ build/bin/swab: src/swab.rs build rustlibs
 true: build/bin/true
 build/bin/true: src/true.c build
 	$(CC) $(CFLAGS) -o $@ src/true.c
+
+.PHONY: zn
+zn: build/bin/zn
+build/bin/zn: src/zn.c build
+	$(CC) $(CFLAGS) -o $@ src/zn.c

src/zn.c

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2024 DTB <trinity@trinity.moe>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ *
+ * This program is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Affero General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option) any
+ * later version.
+ * 
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see https://www.gnu.org/licenses/.
+ */
+
+#include <limits.h> /* _POSIX_MAX_CANON */
+#include <stdio.h> /* fgets(3) */
+#include <string.h> /* strtok(3) */
+#include <sysexits.h> /* EX_OSERR */
+#include <unistd.h> /* fork(2) */
+#include <sys/wait.h> /* wait(2), WIFEXITED, WEXITSTATUS */
+
+static char *sep = " \t\v\n";
+
+static char **
+get_args(char *s) {
+	size_t c = 0;
+	static char *v[10];
+
+	if ((v[c] = strtok(s, sep)) == NULL) { return NULL; }
+
+	while (++c < sizeof v / sizeof *v) {
+		if ((v[c] = strtok(NULL, sep)) == NULL) { return v; }
+	}
+
+	return v;
+}
+
+static char *
+get_line(FILE *stream) {
+	static char buffer[_POSIX_MAX_CANON];
+
+	return fgets(buffer, sizeof *buffer * MAX_CANON, stream);
+}
+
+int main(int argc, char *argv[]) {
+	char **a;
+	char *s;
+
+	while ((s = get_line(stdin)) != NULL) {
+		a = get_args(s);
+		switch (fork()) {
+			case -1: perror(argv[0]); return EX_OSERR;
+			case  0: execvp(a[0], a);
+			default: (void)wait(NULL);
+		}
+	}
+}