From a3183ff88a1aaac66bd49f258fdd02fdeff421ca Mon Sep 17 00:00:00 2001
From: Thomas Voss <thomasvoss@live.com>
Date: Tue, 8 Feb 2022 00:37:20 +0100
Subject: Initial commit

This initial commit includes the following:

 - A gitignore file
 - A license (0-Clause BSD)
 - A Makefile supporting installation
 - A manual page written in mdoc(7)
 - A fully working initial implementation
---
 center.c | 163 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 163 insertions(+)
 create mode 100644 center.c

(limited to 'center.c')

diff --git a/center.c b/center.c
new file mode 100644
index 0000000..ce0d50e
--- /dev/null
+++ b/center.c
@@ -0,0 +1,163 @@
+#define POSIXLY_CORRECT
+#define _POSIX_C_SOURCE 200809L
+
+#include <sys/ioctl.h>
+
+#include <ctype.h>
+#include <err.h>
+#include <errno.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define ESC 033
+
+static void center(FILE *);
+static int cols(void);
+static int utf8len(const char *);
+static int noesclen(const char *);
+static int matchesc(const char *);
+
+extern int optind;
+extern char *optarg;
+
+int rval;
+long width;
+int (*lenfunc)(const char *) = noesclen;
+
+int
+main(int argc, char **argv)
+{
+	int opt;
+	char *endptr;
+
+	while ((opt = getopt(argc, argv, ":elsw:")) != -1) {
+		switch (opt) {
+		case 'e':
+			lenfunc = utf8len;
+			break;
+		case 'w':
+			width = strtol(optarg, &endptr, 0);
+			if (*optarg == '\0' || *endptr != '\0')
+				errx(EXIT_FAILURE, "Invalid integer '%s'", optarg);
+			if (width <= 0)
+				errx(EXIT_FAILURE, "Width must be >0");
+			if (errno == ERANGE || width > INT_MAX)
+				warnx("Potential overflow of given width");
+			break;
+		default:
+			fprintf(stderr, "Usage: %s [-e] [-w width]\n", argv[0]);
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	if (!width && (width = cols()) == -1)
+		errx(EXIT_FAILURE, "Unable to determine output width");
+
+	argc -= optind;
+	argv += optind;
+
+	if (argc == 0)
+		center(stdin);
+	else do {
+		if (strcmp(*argv, "-") == 0)
+			center(stdin);
+		else {
+			FILE *fp;
+			if ((fp = fopen(*argv, "r")) == NULL)
+				errx(EXIT_FAILURE, "fopen");
+			center(fp);
+			fclose(fp);
+		}
+	} while (*++argv);
+
+	return rval;
+}
+
+/* Write the contents of the file pointed to by `fp' center aligned to the standard output */
+void
+center(FILE *fp)
+{
+	char *line = NULL;
+	size_t bs = 0;
+
+	while (getline(&line, &bs, fp) != -1) {
+		int len, tabs = 0;
+		char *match = line;
+
+		while (strchr(match, '\t')) {
+			match++;
+			tabs++;
+		}
+
+		len = lenfunc(line) + tabs * 8 - tabs + 1;
+		printf("%*s", ((int) width - len) / 2 + len, line);
+	}
+	if (ferror(fp)) {
+		warn("getline");
+		rval = EXIT_FAILURE;
+	}
+}
+
+/* Return the column width of the output device if it is a TTY. If it is not a TTY then return -1 */
+int
+cols(void)
+{
+	struct winsize w;
+
+	if (!isatty(STDOUT_FILENO))
+		return -1;
+	if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &w) == -1)
+		err(EXIT_FAILURE, "ioctl");
+
+	return w.ws_col;
+}
+
+/* Return the length of the UTF-8 encoded string `s' in characters, not bytes */
+int
+utf8len(const char *s)
+{
+	int l = 0;
+
+	while (*s)
+		l += (*s++ & 0xC0) != 0x80;
+
+	return l;
+}
+
+/* Return the length of the UTF-8 encoded string `s' in characters, not bytes. Additionally this
+ * function ignores ANSI color escape sequences when computing the length.
+ */
+int
+noesclen(const char *s)
+{
+	int off = 0;
+	const char *d = s;
+
+	while ((d = strchr(d, ESC)) != NULL)
+		off += matchesc(++d);
+	
+	return utf8len(s) + off;
+}
+
+/* Return the length of the ANSI color escape sequence at the beginning of the string `s'. If no
+ * escape sequence is matched then 0 is returned. The local variable `c' is initialized to 3 in order
+ * to account for the leading ESC, the following `[', and the trailing `m'.
+ */
+int
+matchesc(const char *s)
+{
+	int c = 3;
+	
+	if (*s++ != '[')
+		return 0;
+	while (isdigit(*s) || *s == ';') {
+		c++;
+		s++;
+	}
+	
+	return *s == 'm' ? c : 0;
+}
-- 
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