Add conditional support for -v / --verbose

[oweals/busybox.git] / coreutils / tail.c

diff --git a/coreutils/tail.c b/coreutils/tail.c
index 454c2593625d640bbff061d1b51f8fe34a598481..e352ab627b2e86b9e45c6ae59b1b17e4b0dd6ff1 100644 (file)
--- a/coreutils/tail.c
+++ b/coreutils/tail.c
@@ -24,24 +24,24 @@
  * 7) lseek attempted when count==0 even if arg was +0 (from top)
  */
 
+//kbuild:lib-$(CONFIG_TAIL) += tail.o
+
 //usage:#define tail_trivial_usage
 //usage:       "[OPTIONS] [FILE]..."
 //usage:#define tail_full_usage "\n\n"
 //usage:       "Print last 10 lines of each FILE (or stdin) to stdout.\n"
 //usage:       "With more than one FILE, precede each with a filename header.\n"
 //usage:     "\n       -f              Print data as file grows"
-//usage:       IF_FEATURE_FANCY_TAIL(
-//usage:     "\n       -s SECONDS      Wait SECONDS between reads with -f"
-//usage:       )
+//usage:     "\n       -c [+]N[kbm]    Print last N bytes"
 //usage:     "\n       -n N[kbm]       Print last N lines"
+//usage:     "\n       -n +N[kbm]      Start on Nth line and print the rest"
 //usage:       IF_FEATURE_FANCY_TAIL(
-//usage:     "\n       -c N[kbm]       Print last N bytes"
 //usage:     "\n       -q              Never print headers"
+//usage:     "\n       -s SECONDS      Wait SECONDS between reads with -f"
 //usage:     "\n       -v              Always print headers"
+//usage:     "\n       -F              Same as -f, but keep retrying"
 //usage:     "\n"
 //usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
-//usage:     "\nIf N starts with a '+', output begins with the Nth item from the start"
-//usage:     "\nof each file, not from the end."
 //usage:       )
 //usage:
 //usage:#define tail_example_usage
@@ -50,18 +50,12 @@
 
 #include "libbb.h"
 
-static const struct suffix_mult tail_suffixes[] = {
-       { "b", 512 },
-       { "k", 1024 },
-       { "m", 1024*1024 },
-       { "", 0 }
-};
-
 struct globals {
        bool from_top;
        bool exitcode;
 } FIX_ALIASING;
 #define G (*(struct globals*)&bb_common_bufsiz1)
+#define INIT_G() do { } while (0)
 
 static void tail_xprint_header(const char *fmt, const char *filename)
 {
@@ -72,15 +66,6 @@ static void tail_xprint_header(const char *fmt, const char *filename)
 static ssize_t tail_read(int fd, char *buf, size_t count)
 {
        ssize_t r;
-       off_t current;
-       struct stat sbuf;
-
-       /* /proc files report zero st_size, don't lseek them. */
-       if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
-               current = lseek(fd, 0, SEEK_CUR);
-               if (sbuf.st_size < current)
-                       xlseek(fd, 0, SEEK_SET);
-       }
 
        r = full_read(fd, buf, count);
        if (r < 0) {
@@ -101,7 +86,7 @@ static unsigned eat_num(const char *p)
                p++;
                G.from_top = 1;
        }
-       return xatou_sfx(p, tail_suffixes);
+       return xatou_sfx(p, bkm_suffixes);
 }
 
 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
@@ -119,6 +104,9 @@ int tail_main(int argc, char **argv)
 
        int *fds;
        const char *fmt;
+       int prev_fd;
+
+       INIT_G();
 
 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
        /* Allow legacy syntax of an initial numeric option without -n. */
@@ -203,7 +191,7 @@ int tail_main(int argc, char **argv)
                int fd = fds[i];
 
                if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
-                       continue; /* may happen with -E */
+                       continue; /* may happen with -F */
 
                if (nfiles > header_threshhold) {
                        tail_xprint_header(fmt, argv[i]);
@@ -252,14 +240,14 @@ int tail_main(int argc, char **argv)
                 * Used only by +N code ("start from Nth", 1-based): */
                seen = 1;
                newlines_seen = 0;
-               while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
+               while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
                        if (G.from_top) {
                                int nwrite = nread;
                                if (seen < count) {
                                        /* We need to skip a few more bytes/lines */
                                        if (COUNT_BYTES) {
                                                nwrite -= (count - seen);
-                                               seen = count;
+                                               seen += nread;
                                        } else {
                                                char *s = buf;
                                                do {
@@ -321,6 +309,7 @@ int tail_main(int argc, char **argv)
                        xwrite(STDOUT_FILENO, tailbuf, taillen);
                }
        } while (++i < nfiles);
+       prev_fd = fds[i-1];
 
        tailbuf = xrealloc(tailbuf, BUFSIZ);
 
@@ -364,10 +353,23 @@ int tail_main(int argc, char **argv)
                        if (nfiles > header_threshhold) {
                                fmt = header_fmt_str;
                        }
-                       while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
-                               if (fmt) {
+                       for (;;) {
+                               /* tail -f keeps following files even if they are truncated */
+                               struct stat sbuf;
+                               /* /proc files report zero st_size, don't lseek them */
+                               if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
+                                       off_t current = lseek(fd, 0, SEEK_CUR);
+                                       if (sbuf.st_size < current)
+                                               xlseek(fd, 0, SEEK_SET);
+                               }
+
+                               nread = tail_read(fd, tailbuf, BUFSIZ);
+                               if (nread <= 0)
+                                       break;
+                               if (fmt && (fd != prev_fd)) {
                                        tail_xprint_header(fmt, filename);
                                        fmt = NULL;
+                                       prev_fd = fd;
                                }
                                xwrite(STDOUT_FILENO, tailbuf, nread);
                        }