From 50591238eb4e70bf2bca59f536fd4f2253cb57f9 Mon Sep 17 00:00:00 2001
From: Timothy Elliott <tle@holymonkey.com>
Date: Thu, 23 Feb 2012 11:51:13 -0800
Subject: Add tail.

Disabled by default because the -f option is not implemented.
---
 toys/tail.c | 201 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 201 insertions(+)
 create mode 100644 toys/tail.c

diff --git a/toys/tail.c b/toys/tail.c
new file mode 100644
index 00000000..08bae7b6
--- /dev/null
+++ b/toys/tail.c
@@ -0,0 +1,201 @@
+/* vi: set sw=4 ts=4:
+ *
+ * tail.c - copy last lines from input to stdout.
+ *
+ * Copyright 2012 Timothy Elliott <tle@holymonkey.com>
+ *
+ * See http://www.opengroup.org/onlinepubs/009695399/utilities/tail.html
+
+USE_HEAD(NEWTOY(tail, "c:fn:", TOYFLAG_BIN))
+
+config TAIL
+	bool "tail"
+	default n
+	help
+	  usage: tail [-n number] [-c number] [-f] [file...]
+
+	  Copy last lines from files to stdout. If no files listed, copy from
+	  stdin. Filename "-" is a synonym for stdin.
+
+	  -n	Line offset to start copying from. The number may be signed.
+	        When negative, the line offset is counted from the end of the 
+	        file. When positive, the offset is counted from the beginning.
+	        When the sign is omitted, the offset is counted from the end of
+		the file. Defaults to -10.
+
+	  -c    Byte offset to start copying from. As above, may be a positive
+	        or negative signed number.
+
+	  -f   	Continue reading input after reaching the last line of input.
+	        This option is ignored if the input file is not a regular file
+	        or the given file is a FIFO.
+*/
+
+#include "toys.h"
+
+DEFINE_GLOBALS(
+	char *lines_str;
+	char *bytes_str;
+	long lines;
+	long bytes;
+	int file_no;
+)
+
+#define TT this.tail
+
+#define FLAG_n 1
+#define FLAG_f 2
+#define FLAG_c 4
+	
+struct line_list {
+	struct line_list *next;
+	char *data;
+	ssize_t len;
+	long lines;
+};
+
+static void print_after_offset(int fd, long bytes, long lines)
+{
+	ssize_t read_len;
+	long size=sizeof(toybuf);
+	char c;
+	
+	while (bytes > 0 || lines > 0) {
+		if (1>read(fd, &c, 1)) break;
+		bytes--;
+		if (c == '\n') lines--;
+	}
+
+	for (;;) {
+		read_len = xread(fd, toybuf, size);
+		if (read_len<1) break;
+		xwrite(1, toybuf, read_len);
+	}
+}
+
+static void print_last_bytes(int fd, long bytes)
+{
+	char *buf1, *buf2, *temp;
+	ssize_t read_len;
+
+	buf1 = xmalloc(bytes);
+	buf2 = xmalloc(bytes);
+
+	for(;;) {
+		// swap buf1 and buf2
+		temp = buf1;
+		buf1 = buf2;
+		buf2 = temp;
+
+		read_len = readall(fd, buf2, bytes);
+		if (read_len<bytes) break;
+	}
+
+	// output part of buf1 and all of buf2
+	xwrite(1, buf1 + read_len, bytes - read_len);
+	xwrite(1, buf2, read_len);
+
+	if (CFG_TOYBOX_FREE) {
+		free(buf1);
+		free(buf2);
+	}
+}
+
+static void free_line(void *data)
+{
+	struct line_list *list = (struct line_list *)data;
+	free(list->data);
+	free(list);
+}
+
+static void llist_add(struct line_list **head, struct line_list *new)
+{
+	struct line_list *cur = *head;
+
+	new->next = NULL;
+	if (cur) {
+		while (cur->next)
+			cur = cur->next;
+		cur->next = new;
+	} else *head = new;
+}
+
+static void print_last_lines(int fd, long lines)
+{
+	ssize_t i, total=0;
+	long size=sizeof(toybuf);
+	struct line_list *buf=NULL, *cur;
+
+	for (;;) {
+		// read from input and append to buffer list
+		cur = xmalloc(sizeof(struct line_list));
+		memset(cur, 0, sizeof(struct line_list));
+
+		cur->data = xmalloc(size);
+		cur->len = readall(fd, cur->data, size);
+		llist_add(&buf, cur);
+
+		// count newlines in latest input
+		for (i=0; i<cur->len; i++)
+			if (cur->data[i] == '\n') cur->lines++;
+		total += cur->lines;
+
+		// release first buffers if it leaves us enough newlines
+		while (total - buf->lines > lines) {
+			total -= buf->lines;
+			free_line(llist_pop(&buf));
+		}
+		if (cur->len < size) break;
+	}
+	
+	// if last buffer doesn't end in a newline, pretend like it did
+	if (cur->data[cur->len - 1]!='\n') total++;
+	
+	// print out part of the first buffer
+	i = 0;
+	while (total>lines)
+		if (buf->data[i++]=='\n') total--;
+	xwrite(1, buf->data + i, buf->len - i);
+	
+	// print remaining buffers in their entirety
+	for (cur=buf->next; cur; cur=cur->next)
+		xwrite(1, cur->data, cur->len);
+
+	if (CFG_TOYBOX_FREE) llist_free(buf, free_line);
+}
+
+static void do_tail(int fd, char *name)
+{
+	long lines=TT.lines, bytes=TT.bytes;
+
+	if (toys.optc > 1) {
+		// print an extra newline for all but the first file
+		if (TT.file_no++) xprintf("\n");
+		xprintf("==> %s <==\n", name);
+		xflush();
+	}
+
+	if (lines > 0 || bytes > 0) print_after_offset(fd, bytes, lines);
+	else if (bytes < 0) print_last_bytes(fd, bytes * -1);
+	else if (lines < 0) print_last_lines(fd, lines * -1);
+}
+
+long atolx_default_negative(char *str)
+{
+	long val = atolx(str);
+	return str[0] != '+' && str[0] != '-' ? val * -1 : val;
+}
+
+void tail_main(void)
+{
+	// if option -c or -n has no sign then we make it negative
+	if (toys.optflags & FLAG_c)
+		TT.bytes = atolx_default_negative(TT.bytes_str);
+
+	if (toys.optflags & FLAG_n)
+		TT.lines = atolx_default_negative(TT.lines_str);
+	else
+		TT.lines = -10;
+
+	loopfiles(toys.optargs, do_tail);
+}
-- 
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