[hackers] [sbase][PATCH] Add implementation of tac(1)

---
 .gitignore         |  1 +
 Makefile           |  1 +
 README             |  1 +
 libutil/getlines.c |  3 +-
 tac.1              | 22 +++++++++++++++
 tac.c              | 68 ++++++++++++++++++++++++++++++++++++++++++++++
 text.h             |  3 +-
 7 files changed, 97 insertions(+), 2 deletions(-)
 create mode 100644 tac.1
 create mode 100644 tac.c
diff --git a/.gitignore b/.gitignore
index c2504af..daa7189 100644
--- a/.gitignore
+++ b/.gitignore
_AT_@ -77,6 +77,7 @@
 /sponge
 /strings
 /sync
+/tac
 /tail
 /tar
 /tee
diff --git a/Makefile b/Makefile
index 8cfd981..8a4c1ef 100644
--- a/Makefile
+++ b/Makefile
_AT_@ -166,6 +166,7 @@ BIN =\
 	sponge\
 	strings\
 	sync\
+	tac\
 	tail\
 	tar\
 	tee\
diff --git a/README b/README
index cadc89e..f16eab8 100644
--- a/README
+++ b/README
_AT_@ -118,6 +118,7 @@ The following tools are implemented:
 0=*|x sponge          .
 0#*|o strings         .
 0=*|x sync            .
+0=* x tac             .
 0=*|o tail            .
 0=*|x tar             .
 0=*|o tee             .
diff --git a/libutil/getlines.c b/libutil/getlines.c
index cef9a61..34392f7 100644
--- a/libutil/getlines.c
+++ b/libutil/getlines.c
_AT_@ -23,7 +23,8 @@ getlines(FILE *fp, struct linebuf *b)
 		b->lines[b->nlines - 1].len = linelen;
 	}
 	free(line);
-	if (b->lines && b->nlines && linelen && b->lines[b->nlines - 1].data[linelen - 1] != '\n') {
+	b->nolf = b->lines && b->nlines && linelen && b->lines[b->nlines - 1].data[linelen - 1] != '\n';
+	if (b->nolf) {
 		b->lines[b->nlines - 1].data = erealloc(b->lines[b->nlines - 1].data, linelen + 2);
 		b->lines[b->nlines - 1].data[linelen] = '\n';
 		b->lines[b->nlines - 1].data[linelen + 1] = '\0';
diff --git a/tac.1 b/tac.1
new file mode 100644
index 0000000..0274fc6
--- /dev/null
+++ b/tac.1
_AT_@ -0,0 +1,22 @@
+.Dd 2024-02-25
+.Dt TAC 1
+.Os sbase
+.Sh NAME
+.Nm tac
+.Nd concatenate files and print them in reverse
+.Sh SYNOPSIS
+.Nm
+.Op Ar file ...
+.Sh DESCRIPTION
+.Nm
+reads each
+.Ar file
+in sequence and prints their lines in reverse order.
+The files are still printed in order.
+If no
+.Ar file
+is given,
+.Nm
+reads from stdin.
+.Sh SEE ALSO
+.Xr cat 1
diff --git a/tac.c b/tac.c
new file mode 100644
index 0000000..5dca474
--- /dev/null
+++ b/tac.c
_AT_@ -0,0 +1,68 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "text.h"
+#include "util.h"
+
+static void
+usage(void)
+{
+	eprintf("usage: %s [file ...]\n", argv0);
+}
+
+static void
+tac(FILE *fp)
+{
+	struct linebuf buf = EMPTY_LINEBUF;
+	struct line line;
+	getlines(fp, &buf);
+
+	if (buf.nolf) {
+		/* If the last line is not LF-terminated, the
+		 * first output line should not be either */
+		 buf.nolf--;
+		 buf.lines[buf.nlines - 1].len--;
+	}
+
+	while (buf.nlines--) {
+		line = buf.lines[buf.nlines];
+		fwrite(line.data, 1, line.len, stdout);
+		free(line.data);
+	}
+	free(buf.lines);
+}
+
+int
+main(int argc, char *argv[])
+{
+	FILE *fp;
+	int ret = 0;
+
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
+
+	if (!argc) {
+		tac(stdin);
+	} else {
+		for (; *argv; argc--, argv++) {
+			if (!strcmp(*argv, "-")) {
+				*argv = "<stdin>";
+				fp = stdin;
+			} else if (!(fp = fopen(*argv, "r"))) {
+				weprintf("fopen %s:", *argv);
+				ret = 1;
+				continue;
+			}
+			tac(fp);
+			if (fp != stdin && fshut(fp, *argv))
+				ret = 1;
+		}
+	}
+
+	ret |= fshut(stdin, "<stdin>") | fshut(stdout, "<stdout>");
+
+	return ret;
+}
diff --git a/text.h b/text.h
index 9858592..dcebbdc 100644
--- a/text.h
+++ b/text.h
_AT_@ -9,8 +9,9 @@ struct linebuf {
 	struct line *lines;
 	size_t nlines;
 	size_t capacity;
+	int nolf;
 };
-#define EMPTY_LINEBUF {NULL, 0, 0,}
+#define EMPTY_LINEBUF {NULL, 0, 0, 0,}
 void getlines(FILE *, struct linebuf *);
 
 int linecmp(struct line *, struct line *);
-- 
2.44.0