tail(1p): initial commit & libyac: fixed build

Makefile

@@ -10,26 +10,26 @@
 PREFIX=/usr/local
 CFLAGS=-O3 -s -Wl,-z,noseparate-code,-z,nosectionheader -flto -Lbuild -lyac
 
-build: build_dir lib cat false tail true
+build: build_dir cat false tail true
 
 clean: build_dir
 	rm -rf build/
 
-cat: build_dir
+cat: build_dir lib
 	cc $(CFLAGS) -o build/cat src/cat.c
 
-false: build_dir
+false: build_dir lib
 	cc $(CFLAGS) -o build/false src/false.c
 
-tail: build_dir
+tail: build_dir lib
 	cc $(CFLAGS) -o build/tail src/tail.c
 
-true: build_dir
+true: build_dir lib
 	cc $(CFLAGS) -o build/true src/true.c
 
 lib:
-	cc -c -fPIC $(CFLAGS) -o build/yac.o src/yac.c
-	cc $(CFLAGS) -shared -o build/libyac.so build/yac.o
+	cc $(CFLAGS) -c -fPIC -o build/yac.o src/yac.c
+	cc -shared -o build/libyac.so build/yac.o
 
 build_dir:
 	mkdir -p build

src/tail.c

@@ -0,0 +1,134 @@
+/*
+ * Copyright (c) 2023 Emma Tebibyte <emma@tebibyte.media>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ *
+ * This file is part of YAC coreutils.
+ *
+ * YAC coreutils 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.
+ * 
+ * YAC coreutils 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 <errno.h>
+#include <sysexits.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "yac.h"
+
+void tail(FILE *file, bool c, bool f, long num) {
+	long offset;
+	if (c) { fseek(file, offset, SEEK_END); }
+	else {
+		for 
+	}
+
+}
+
+int main(int argc, char *argv[]) {
+	bool c = false;
+	bool f = false;
+	bool n = false;
+	long num;
+	int opt;
+	int i;
+
+	extern int optind;
+	while ((opt = getopt(argc, argv, "c:fn:")) != -1) {
+		switch (opt) {
+		/*
+		 * From tail(1p):
+		 *
+		 * -c number The application shall ensure that the number option-argument
+		 *           is a decimal integer, optionally including a sign.  The sign
+		 *           shall affect the location in the file, measured in bytes, to
+		 *           begin the copying:
+		 *
+		 *                  ┌─────┬────────────────────────────────────────┐
+		 *                  │Sign │             Copying Starts             │
+		 *                  ├─────┼────────────────────────────────────────┤
+		 *                  │ +   │ Relative to the beginning of the file. │
+		 *                  │ -   │ Relative to the end of the file.       │
+		 *                  │none │ Relative to the end of the file.       │
+		 *                  └─────┴────────────────────────────────────────┘
+		 *           The application shall ensure that if the sign of the number
+		 *           option-argument is '+', the number option-argument is a non-
+		 *           zero decimal integer.
+		 *
+		 *           The origin for counting shall be 1; that is, -c +1 represents
+		 *           the first byte of the file, -c -1 the last.
+		 *
+		 * -f        If the input file is a regular file or if the file operand
+		 *           specifies a FIFO, do not terminate after the last line of the
+		 *           input file has been copied, but read and copy further bytes
+		 *           from the input file when they become available. If no file
+		 *           operand is specified and standard input is a pipe or FIFO,
+		 *           the -f option shall be ignored. If the input file is not a
+		 *           FIFO, pipe, or regular file, it is unspecified whether or not
+		 *           the -f option shall be ignored.
+		 *
+		 * -n number This option shall be equivalent to -c number, except the
+		 *  starting location in the file shall be measured in lines
+		 *  instead of bytes. The origin for counting shall be 1; that
+		 *  is, -n +1 represents the first line of the file, -n -1 the
+		 *  last.
+		 *
+		 *  If neither -c nor -n is specified, -n 10 shall be assumed.
+		 */
+			case 'c':
+				c = true;
+				num = (long)optarg;
+				break;
+			case 'f':
+				f = true;
+			case 'n':
+				n = true;
+				num = (long)optarg;
+				break;
+			default:
+				fprintf(
+					stderr,
+					"Usage: %s (-f) [-c characters] [-n lines] file...\n",
+					argv[0]
+				);
+				return EX_USAGE;
+		}
+	}
+
+	if (!n && !c) {
+		num = 10;
+	} else if (n && c) {
+		fprintf(
+			stderr,
+			"Usage: %s (-f) [-c characters] [-n lines] file...\n",
+			argv[0]
+		);
+		return EX_USAGE;
+	}
+
+	if (optind = argc) {
+		tail(stdin, c, f, num);
+	}
+	
+	FILE *file;
+
+	for (i = optind; i < argc; i++) {
+		file = rfile(argv0, argv[i]);
+		if file != NULL {
+			tail(file, c, f, num);
+			if (file != stdin) { fclose(file); }
+		}
+	}
+
+	return EX_OK;
+}