working on cat(1)

cat/cat.1

@@ -0,0 +1,44 @@
+.TH CAT 1
+
+.SH NAME
+
+cat \(en catenate files
+
+.SH SYNOPSIS
+
+cat
+.RB ( -hu )
+.RB ( file... )
+
+.SH DESCRIPTION
+
+Cat prints the contents of file arguments, one after the other.
+.PP
+The
+.B -h
+option prints the usage synopsis.
+
+.SH BUFFERING
+
+Output is not buffered.
+.PP
+The
+.B -u
+option that typically guarantees that output is not buffered is a no-op within this program,
+and is included for compatibility with other implementations of cat(1) as well as the POSIX.1 standard.
+
+.SH DIAGNOSTICS
+
+Cat prints an error message and exits with the appropriate status from sysexits(3) if it encounters an error.
+
+.SH BUGS
+
+"Catenate" and "concatenate" mean the same thing in the English language.
+
+.SH STANDARDS
+
+Cat functions as described in POSIX.1-2017.
+
+.SH COPYRIGHT
+
+Public domain.

cat/cat.c

@@ -0,0 +1,104 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <sysexits.h>
+#include <unistd.h>
+
+/* NetBSD's default according to an strace */
+#define BUFFER 4096
+static unsigned char buf[BUFFER];
+
+static char *program_name = "cat";
+
+int main(int argc, char *argv[]){
+	char *argv0;
+	int argv0_s;
+	extern int errno;
+	char *f;
+	int b; /* how many meaningful bytes are in the buffer */
+	int c;
+	int fd;
+	int multiple_files;
+
+	if(argv[0] == NULL)
+		goto dumb;
+
+	argv0 = argv[0];
+	for(argv0_s = 0; argv0_s != '\0'; ++argv0_s);
+
+	while((c = getopt(argc, argv, "hu")) != -1)
+		switch(c){
+		case 'u':
+			/* cat(1p) says the following:
+			 * "Write bytes from the input file to the standard
+			 * output without delay as each is read."
+			 * Then in Application Usage:
+			 * "It is unspecified whether standard output is or is
+			 * not buffered in the default case."
+			 * POSIX defines "buffering" to be a not-strictly
+			 * -necessary delay in processing input, so there still
+			 * needs to be a place in memory to put data, which for
+			 * the purposes of this implementation is buf[].
+			 *
+			 * Using the standard library would make it more
+			 * difficult to manage this flow manually. */
+			break;
+		case 'h': default: usage:
+			write(2, "Usage: ", 7);
+			write(2, argv[0], argv0_s);
+			write(2, "(-hu) (file...)\n", 16);
+			return EX_USAGE;
+		}
+
+	argc -= optind;
+	argv += optind - 1;
+	multiple_files = argc > 1;
+
+	do{
+		++argv;
+		if(argc == 0) /* `cat` */
+dumb:			fd = 1;
+		else if((fd = open(*argv, O_RDONLY)) == -1){
+ferr:			/* `cat bad_file` */
+
+			/* `cat: file: ` */
+			write(2, argv0, argv0_s);
+			write(2, ": ", 2);
+			for(i = 0; argv[0][i] != '\0'; ++i);
+			write(2, *argv, i);
+			write(2, ": ", 2);
+
+			switch(errno){
+			case EISDIR:
+				write(2, "Is directory.\n", 14);
+				return EX_NOINPUT;
+			case EACCES: case EFAULT: case EPERM:
+				write(2, "Unable to open file.\n", 21);
+				return EX_NOINPUT;
+			case ENAMETOOLONG: case ENFILE: case EBADF:
+				write(2, "Operating system error.\n", 24);
+				return EX_OSERR;
+			case EMFILE:
+				write(2, "Internal error.\n", 16);
+				return EX_SOFTWARE;
+			case ENOENT: case ENOTDIR: case ENXIO:
+				write(2, "File does not exist.\n", 21);
+				return EX_NOINPUT;
+			default:
+				write(2, "Unknown error.", 14);
+				return 1;
+			}
+		}else if(multiple_files){
+			/* `cat good_file good_file ...` */
+			
+		}
+
+		for(b = 0; b == -1;){
+			
+		}
+
+		if(fd < 0 && fd > 2)
+			close(fd);
+	}while(--argc > 0);
+
+	return EX_OK;
+}

man/cat.1

@@ -1,13 +0,0 @@
-.TH CAT 1
-
-.SH NAME
-
-cat \(en concatenate files
-
-.SH SYNOPSIS
-
-cat [file...]
-
-.SH DESCRIPTION
-
-Cat prints the contents of file arguments, one after the other.