head: support -n -NUM and -c -NUM

function                                             old     new   delta
head_main                                            406     832    +426
packed_usage                                       29234   29252     +18
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 444/0)             Total: 444 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/coreutils/head.c b/coreutils/head.c
index 598fccb..291e1ce 100644 (file)
--- a/coreutils/head.c
+++ b/coreutils/head.c
@@ -21,7 +21,8 @@
 //usage:       "With more than one FILE, precede each with a filename header.\n"
 //usage:     "\n       -n N[kbm]       Print first N lines"
 //usage:       IF_FEATURE_FANCY_HEAD(
-//usage:     "\n       -c N[kbm]       Print first N bytes"
+//usage:     "\n       -n -N[kbm]      Print all except N last lines"
+//usage:     "\n       -c [-]N[kbm]    Print first N bytes"
 //usage:     "\n       -q              Never print headers"
 //usage:     "\n       -v              Always print headers"
 //usage:       )
@@ -38,6 +39,110 @@
 
 /* This is a NOEXEC applet. Be very careful! */
 
+#if !ENABLE_FEATURE_FANCY_HEAD
+# define print_first_N(fp,count,bytes) print_first_N(fp,count)
+#endif
+static void
+print_first_N(FILE *fp, unsigned long count, bool count_bytes)
+{
+#if !ENABLE_FEATURE_FANCY_HEAD
+       const int count_bytes = 0;
+#endif
+       while (count) {
+               int c = getc(fp);
+               if (c == EOF)
+                       break;
+               if (count_bytes || (c == '\n'))
+                       --count;
+               putchar(c);
+       }
+}
+
+#if ENABLE_FEATURE_FANCY_HEAD
+static void
+print_except_N_last_bytes(FILE *fp, unsigned count)
+{
+       unsigned char *circle = xmalloc(++count);
+       unsigned head = 0;
+       for(;;) {
+               int c;
+               c = getc(fp);
+               if (c == EOF)
+                       goto ret;
+               circle[head++] = c;
+               if (head == count)
+                       break;
+       }
+       for (;;) {
+               int c;
+               if (head == count)
+                       head = 0;
+               putchar(circle[head]);
+               c = getc(fp);
+               if (c == EOF)
+                       goto ret;
+               circle[head] = c;
+               head++;
+       }
+ ret:
+       free(circle);
+}
+
+static void
+print_except_N_last_lines(FILE *fp, unsigned count)
+{
+       char **circle = xzalloc((++count) * sizeof(circle[0]));
+       unsigned head = 0;
+       for(;;) {
+               char *c;
+               c = xmalloc_fgets(fp);
+               if (!c)
+                       goto ret;
+               circle[head++] = c;
+               if (head == count)
+                       break;
+       }
+       for (;;) {
+               char *c;
+               if (head == count)
+                       head = 0;
+               fputs(circle[head], stdout);
+               c = xmalloc_fgets(fp);
+               if (!c)
+                       goto ret;
+               free(circle[head]);
+               circle[head++] = c;
+       }
+ ret:
+       head = 0;
+       for(;;) {
+               free(circle[head++]);
+               if (head == count)
+                       break;
+       }
+       free(circle);
+}
+#else
+/* Must never be called */
+void print_except_N_last_bytes(FILE *fp, unsigned count);
+void print_except_N_last_lines(FILE *fp, unsigned count);
+#endif
+
+#if !ENABLE_FEATURE_FANCY_HEAD
+# define eat_num(negative_N,p) eat_num(p)
+#endif
+static unsigned long
+eat_num(bool *negative_N, const char *p)
+{
+#if ENABLE_FEATURE_FANCY_HEAD
+       if (*p == '-') {
+               *negative_N = 1;
+               p++;
+       }
+#endif
+       return xatoul_sfx(p, head_tail_suffixes);
+}
+
 static const char head_opts[] ALIGN1 =
        "n:"
 #if ENABLE_FEATURE_FANCY_HEAD
@@ -52,8 +157,13 @@ int head_main(int argc, char **argv)
 {
        unsigned long count = 10;
 #if ENABLE_FEATURE_FANCY_HEAD
-       int count_bytes = 0;
        int header_threshhold = 1;
+       bool count_bytes = 0;
+       bool negative_N = 0;
+#else
+# define header_threshhold 1
+# define count_bytes       0
+# define negative_N        0
 #endif
        FILE *fp;
        const char *fmt;
@@ -68,7 +178,7 @@ int head_main(int argc, char **argv)
        ) {
                --argc;
                ++argv;
-               p = (*argv) + 1;
+               p = argv[0] + 1;
                goto GET_COUNT;
        }
 #endif
@@ -92,7 +202,7 @@ int head_main(int argc, char **argv)
 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_HEAD
  GET_COUNT:
 #endif
-                       count = xatoul_sfx(p, head_tail_suffixes);
+                       count = eat_num(&negative_N, p);
                        break;
                default:
                        bb_show_usage();
@@ -105,39 +215,35 @@ int head_main(int argc, char **argv)
                *--argv = (char*)"-";
 
        fmt = header_fmt_str + 1;
-#if ENABLE_FEATURE_FANCY_HEAD
        if (argc <= header_threshhold) {
+#if ENABLE_FEATURE_FANCY_HEAD
                header_threshhold = 0;
-       }
 #else
-       if (argc <= 1) {
                fmt += 11; /* "" */
-       }
-       /* Now define some things here to avoid #ifdefs in the code below.
-        * These should optimize out of the if conditions below. */
-#define header_threshhold   1
-#define count_bytes         0
 #endif
+       }
+       if (negative_N) {
+               if (count >= INT_MAX / sizeof(char*))
+                       bb_error_msg("count is too big: %lu", count);
+       }
 
        do {
                fp = fopen_or_warn_stdin(*argv);
                if (fp) {
-                       unsigned long i;
-
                        if (fp == stdin) {
                                *argv = (char *) bb_msg_standard_input;
                        }
                        if (header_threshhold) {
                                printf(fmt, *argv);
                        }
-                       i = count;
-                       while (i) {
-                               int c = getc(fp);
-                               if (c == EOF)
-                                       break;
-                               if (count_bytes || (c == '\n'))
-                                       --i;
-                               putchar(c);
+                       if (negative_N) {
+                               if (count_bytes) {
+                                       print_except_N_last_bytes(fp, count);
+                               } else {
+                                       print_except_N_last_lines(fp, count);
+                               }
+                       } else {
+                               print_first_N(fp, count, count_bytes);
                        }
                        die_if_ferror_stdout();
                        if (fclose_if_not_stdin(fp)) {