| /* 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_TAIL(NEWTOY(tail, "fc-n-", TOYFLAG_BIN)) |
| |
| config TAIL |
| bool "tail" |
| default y |
| help |
| usage: tail [-n|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 output the last X lines (default 10), +X counts from start. |
| -c output the last X bytes, +X counts from start |
| -f follow file, waiting for more data to be appended |
| |
| config TAIL_SEEK |
| bool "tail seek support" |
| default y |
| depends on TAIL |
| help |
| This version uses lseek, which is faster on large files. |
| */ |
| |
| #include "toys.h" |
| |
| DEFINE_GLOBALS( |
| long lines; |
| long bytes; |
| |
| int file_no; |
| ) |
| |
| #define TT this.tail |
| |
| #define FLAG_n 1 |
| #define FLAG_c 2 |
| #define FLAG_f 4 |
| |
| struct line_list { |
| struct line_list *next, *prev; |
| char *data; |
| int len; |
| }; |
| |
| static struct line_list *get_chunk(int fd, int len) |
| { |
| struct line_list *line = xmalloc(sizeof(struct line_list)+len); |
| |
| line->data = ((char *)line) + sizeof(struct line_list); |
| line->len = readall(fd, line->data, len); |
| |
| if (line->len < 1) { |
| free(line); |
| return 0; |
| } |
| |
| return line; |
| } |
| |
| static void dump_chunk(void *ptr) |
| { |
| struct line_list *list = ptr; |
| xwrite(1, list->data, list->len); |
| free(list); |
| } |
| |
| // Reading through very large files is slow. Using lseek can speed things |
| // up a lot, but isn't applicable to all input (cat | tail). |
| // Note: bytes and lines are negative here. |
| static int try_lseek(int fd, long bytes, long lines) |
| { |
| struct line_list *list = 0, *temp; |
| int flag = 0, chunk = sizeof(toybuf); |
| ssize_t pos = lseek(fd, 0, SEEK_END); |
| |
| // If lseek() doesn't work on this stream, return now. |
| if (pos<0) return 0; |
| |
| // Seek to the right spot, output data from there. |
| if (bytes) { |
| if (lseek(fd, bytes, SEEK_END)<0) lseek(fd, 0, SEEK_SET); |
| xsendfile(fd, 1); |
| return 1; |
| } |
| |
| // Read from end to find enough lines, then output them. |
| |
| bytes = pos; |
| while (lines && pos) { |
| int offset; |
| |
| // Read in next chunk from end of file |
| if (chunk>pos) chunk = pos; |
| pos -= chunk; |
| if (pos != lseek(fd, pos, SEEK_SET)) { |
| perror_msg("seek failed"); |
| break; |
| } |
| if (!(temp = get_chunk(fd, chunk))) break; |
| if (list) list->next = temp; |
| list = temp; |
| |
| // Count newlines in this chunk. |
| offset = list->len; |
| while (offset--) { |
| // If the last line ends with a newline, that one doesn't count. |
| if (!flag) { |
| flag++; |
| |
| continue; |
| } |
| |
| // Start outputting data right after newline |
| if (list->data[offset] == '\n' && !++lines) { |
| offset++; |
| list->data += offset; |
| list->len -= offset; |
| |
| break; |
| } |
| } |
| } |
| |
| // Output stored data |
| llist_free(list, dump_chunk); |
| |
| // In case of -f |
| lseek(fd, bytes, SEEK_SET); |
| return 1; |
| } |
| |
| // Called for each file listed on command line, and/or stdin |
| static void do_tail(int fd, char *name) |
| { |
| long bytes = TT.bytes, lines = TT.lines; |
| |
| if (toys.optc > 1) { |
| if (TT.file_no++) xputc('\n'); |
| xprintf("==> %s <==\n", name); |
| } |
| |
| // Are we measuring from the end of the file? |
| |
| if (bytes<0 || lines<0) { |
| struct line_list *list = 0, *new; |
| |
| // The slow codepath is always needed, and can handle all input, |
| // so make lseek support optional. |
| if (CFG_TAIL_SEEK && try_lseek(fd, bytes, lines)); |
| |
| // Read data until we run out, keep a trailing buffer |
| else for (;;) { |
| int len, count; |
| char *try; |
| |
| if (!(new = get_chunk(fd, sizeof(toybuf)))) break; |
| // append in order |
| dlist_add_nomalloc((struct double_list **)&list, |
| (struct double_list *)new); |
| |
| // Measure new chunk, discarding extra data from buffer |
| len = new->len; |
| try = new->data; |
| for (count=0; count<len; count++) { |
| if ((toys.optflags & FLAG_c) && bytes) { |
| bytes++; |
| continue; |
| } |
| |
| if (lines) { |
| if(try[count] != '\n') continue; |
| if (lines<0) { |
| if (!++lines) ++lines; |
| continue; |
| } |
| } |
| |
| // Time to discard data; given that bytes and lines were |
| // nonzero coming in, we can't discard too much if we're |
| // measuring right. |
| do { |
| char c = *(list->data++); |
| if (!(--list->len)) { |
| struct line_list *next = list->next; |
| list->prev->next = next; |
| list->next->prev = list->prev; |
| free(list); |
| list = next; |
| } |
| if (c == '\n') break; |
| } while (lines); |
| } |
| } |
| |
| // Output/free the buffer. |
| llist_free(list, dump_chunk); |
| |
| // Measuring from the beginning of the file. |
| } else for (;;) { |
| int len, offset = 0; |
| |
| // Error while reading does not exit. Error writing does. |
| len = read(fd, toybuf, sizeof(toybuf)); |
| if (len<1) break; |
| while (bytes > 1 || lines > 1) { |
| bytes--; |
| if (toybuf[offset++] == '\n') lines--; |
| if (offset >= len) break; |
| } |
| if (offset<len) xwrite(1, toybuf+offset, len-offset); |
| } |
| |
| // -f support: cache name/descriptor |
| } |
| |
| void tail_main(void) |
| { |
| // if nothing specified, default -n to -10 |
| if (!(toys.optflags&(FLAG_n|FLAG_c))) TT.lines = -10; |
| |
| loopfiles(toys.optargs, do_tail); |
| |
| // do -f stuff |
| } |