Add readlink

Signed-off-by: Christoph Lohmann <20h@r-36.net>

readlink.c

@@ -0,0 +1,55 @@
+/* See LICENSE file for copyright and license details. */
+#include <unistd.h>
+#include <errno.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "util.h"
+
+static void
+usage(void)
+{
+	eprintf("usage: %s [-fn] file\n", argv0);
+	exit(1);
+}
+
+int
+main(int argc, char *argv[])
+{
+	char buf[PATH_MAX];
+	bool nflag = false;
+	bool fflag = false;
+
+	ARGBEGIN {
+	case 'f':
+		fflag = true;
+		break;
+	case 'n':
+		nflag = true;
+		break;
+	default:
+		usage();
+	} ARGEND;
+
+	if (argc != 1)
+		usage();
+
+	if (strlen(argv[0]) > PATH_MAX - 1)
+		exit(1);
+
+	if (fflag) {
+		if (realpath(argv[0], buf) == NULL)
+			exit(1);
+	} else {
+		if (readlink(argv[0], buf, sizeof(buf)) < 0)
+			exit(1);
+	}
+
+	printf("%s", buf);
+	if (!nflag)
+		putchar('\n');
+
+	return 0;
+}