add tail

Makefile

@@ -1,8 +1,10 @@
 include config.mk
 
-LIB = util/afgets.o util/agetcwd.o util/enmasse.o util/eprintf.o util/recurse.o
+LIB = util/afgets.o util/agetcwd.o util/concat.o util/enmasse.o util/eprintf.o \
+      util/recurse.o
 SRC = basename.c cat.c chown.c date.c dirname.c echo.c false.c grep.c head.c \
-      ln.c ls.c mkdir.c mkfifo.c pwd.c rm.c sleep.c tee.c touch.c true.c wc.c
+      ln.c ls.c mkdir.c mkfifo.c pwd.c rm.c sleep.c tail.c tee.c touch.c \
+      true.c wc.c
 OBJ = $(SRC:.c=.o) $(LIB)
 BIN = $(SRC:.c=)
 MAN = $(SRC:.c=.1)

basename.1

@@ -13,4 +13,5 @@ with any leading path components, and the
 .IR suffix ,
 removed.
 .SH SEE ALSO
+.IR dirname (1),
 .IR basename (3)

cat.c

@@ -2,10 +2,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include "text.h"
 #include "util.h"
 
-static void cat(FILE *, const char *);
-
 int
 main(int argc, char *argv[])
 {
@@ -14,25 +13,12 @@ main(int argc, char *argv[])
 	if(getopt(argc, argv, "") != -1)
 		exit(EXIT_FAILURE);
 	if(optind == argc)
-		cat(stdin, "<stdin>");
+		concat(stdin, "<stdin>", stdout, "<stdout>");
 	else for(; optind < argc; optind++) {
 		if(!(fp = fopen(argv[optind], "r")))
 			eprintf("fopen %s:", argv[optind]);
-		cat(fp, argv[optind]);
+		concat(fp, argv[optind], stdout, "<stdout>");
 		fclose(fp);
 	}
 	return EXIT_SUCCESS;
 }
-
-void
-cat(FILE *fp, const char *str)
-{
-	char buf[BUFSIZ];
-	size_t n;
-
-	while((n = fread(buf, 1, sizeof buf, fp)) > 0)
-		if(fwrite(buf, 1, n, stdout) != n)
-			eprintf("<stdout>: write error:");
-	if(ferror(fp))
-		eprintf("%s: read error:", str);
-}

dirname.1

@@ -10,4 +10,5 @@ prints the
 .I string
 with its final path component removed.
 .SH SEE ALSO
+.IR basename (1),
 .IR dirname (3)

head.1

@@ -14,3 +14,5 @@ reads from stdin.
 .TP
 .BI \-n " lines"
 outputs the given number of lines.
+.SH SEE ALSO
+.IR tail (1)

tail.1

@@ -0,0 +1,20 @@
+.TH TAIL 1 sbase\-VERSION
+.SH NAME
+tail \- output last part of a file
+.SH SYNOPSIS
+.B tail
+.RB [ \-n
+.IR lines ]
+.RI [ file ]
+.SH DESCRIPTION
+.B tail
+writes the first 10 lines of the file to stdout.  If no file is given, tail
+reads from stdin.
+.SH OPTIONS
+.TP
+.BI \-n " lines"
+outputs the given number of lines.  If
+.I lines
+begins with '+' it is used as an offset from the beginning of the file.
+.SH SEE ALSO
+.IR head (1)

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);
+}

text.h

@@ -1,3 +1,4 @@
 /* See LICENSE file for copyright and license details. */
 
-char *afgets(char **p, size_t *size, FILE *fp);
+char *afgets(char **, size_t *, FILE *);
+void concat(FILE *, const char *, FILE *, const char *);

util/concat.c

@@ -0,0 +1,17 @@
+/* See LICENSE file for copyright and license details. */
+#include <stdio.h>
+#include "../text.h"
+#include "../util.h"
+
+void
+concat(FILE *fp1, const char *s1, FILE *fp2, const char *s2)
+{
+	char buf[BUFSIZ];
+	size_t n;
+
+	while((n = fread(buf, 1, sizeof buf, fp1)) > 0)
+		if(fwrite(buf, 1, n, fp2) != n)
+			eprintf("%s: write error:", s2);
+	if(ferror(fp1))
+		eprintf("%s: read error:", s1);
+}