add tail

tail.c

@@ -0,0 +1,80 @@
+/* See LICENSE file for copyright and license detaketails. */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "text.h"
+#include "util.h"
+
+static void dropinit(FILE *, const char *, long);
+static void taketail(FILE *, const char *, long);
+
+static void (*tail)(FILE *, const char *, long) = taketail;
+
+int
+main(int argc, char *argv[])
+{
+	char *end, c;
+	long n = 10;
+	FILE *fp;
+
+	while((c = getopt(argc, argv, "n:")) != -1)
+		switch(c) {
+		case 'n':
+			n = abs(strtol(optarg, &end, 0));
+			if(*end != '\0')
+				eprintf("%s: not a number\n", optarg);
+			if(optarg[0] == '+')
+				tail = dropinit;
+			break;
+		default:
+			exit(EXIT_FAILURE);
+		}
+	if(optind == argc)
+		tail(stdin, "<stdin>", n);
+	else if(optind == argc-1) {
+		if(!(fp = fopen(argv[optind], "r")))
+			eprintf("fopen %s:", argv[optind]);
+		tail(fp, argv[optind], n);
+		fclose(fp);
+	}
+	else
+		eprintf("usage: %s [-n lines] [file]\n", argv[0]);
+
+	return EXIT_SUCCESS;
+}
+
+void
+dropinit(FILE *fp, const char *str, long n)
+{
+	char buf[BUFSIZ];
+	long i = 0;
+
+	while(i < n && fgets(buf, sizeof buf, fp))
+		if(buf[strlen(buf)-1] == '\n')
+			i++;
+	concat(fp, str, stdout, "<stdout>");
+}
+
+void
+taketail(FILE *fp, const char *str, long n)
+{
+	char **ring;
+	long i, j;
+	size_t *size;
+
+	if(!(ring = calloc(n, sizeof *ring)) || !(size = calloc(n, sizeof *size)))
+		eprintf("calloc:");
+	for(i = j = 0; afgets(&ring[i], &size[i], fp); i = j = (i+1)%n)
+		;
+
+	do {
+		if(ring[j])
+			fputs(ring[j], stdout);
+	} while((j = (j+1)%n) != i);
+	free(ring);
+	free(size);
+
+	if(ferror(fp))
+		eprintf("%s: read error:", str);
+}