Added my implementation of unixtime.

This implementation has very few reasonable code (call atol() and ctime()),
but has some nice standard program stuff (parse options, print help, ...).

unixtime.c

@@ -0,0 +1,138 @@
+/*
+ * unixtime.c
+ */
+
+#include <libgen.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sysexits.h>
+#include <time.h>
+
+/* symbols */
+#define TRUE 1
+#define FALSE 0
+#define VERSION "0.1"
+
+/* prototypes */
+int  print_version(void);
+int  print_help(void);
+
+/* definition of extern objects */
+char       *progname;
+const char *version  = VERSION;
+
+/*
+ * main
+ */
+int main(int argc, char** argv) {
+	int			i;
+	int			j;
+	char		c;
+	char		*p;
+	size_t      l;
+	time_t		t = 0;
+	struct tm	*tm;
+
+	/* Store program name without path
+	 * (will be used in e.g. error messages) */
+	if( (progname = strdup(basename(argv[0]))) == NULL ) {
+		fprintf(stderr, "%s: ", basename(argv[0]));
+		perror(NULL);
+		exit(EX_OSERR);
+	}
+
+	/* Parse command line options */
+	for( i = 1 ; i < argc ; i++ ) {
+		if(!strncmp("--", argv[i], 2)) {
+		/* Current argument is a GNU long option */
+			if(!strcmp(       "--help", argv[i])) {
+				print_help();
+				exit(EX_OK);
+			} else if(!strcmp("--version", argv[i])) {
+				print_version();
+				exit(EX_OK);
+			} else {
+				fprintf(stderr, "%s: invalid option: %s\n", progname, argv[i]);
+				fprintf(stderr, "Try '%s -h' for help.\n", progname);
+				exit(EX_USAGE);
+			}
+		} else if(!strncmp("-", argv[i], 1)) {
+		/* Current argument is one or more short options */
+			p = argv[i];
+			for( j = 1 ; (c = p[j]) != '\0' ; j++) {
+				switch(c) {
+				case 'h':
+					print_help();
+					exit(EX_OK);
+					break;
+				case 'V':
+					print_version();
+					exit(EX_OK);
+					break;
+				default:
+					fprintf(stderr, "%s: invalid option: %c\n", progname, c);
+					fprintf(stderr, "Try '%s -h' for help.\n", progname);
+					exit(EX_USAGE);
+				}
+			}
+		} else {
+			/* This is the first argument, that is not an option. 
+			 * It will be taken as timestamp. */
+			t = atol(argv[i]);
+			l = strlen(argv[i]);
+			if((p = malloc(l + 1)) != NULL) {
+				snprintf(p, l + 1, "%d", t);
+				if(strcmp(argv[i], p)) {
+					fprintf(stderr, "%s: not numeric: %s\n", progname, 
+						argv[i]);
+					exit(EX_DATAERR);
+				}
+				free(p);
+			} else {
+				fprintf(stderr, "%s: Warning: cannot allocate memory"
+					" to do numeric test on input.\n", progname);
+			}
+			break;
+		}
+	} 		
+
+	p = ctime((& t));
+	if(p == NULL) {
+		fprintf(stderr, "%s: unrecognized date '%d'.\n", progname, time);
+		exit(EX_DATAERR);
+	}
+	fputs(p, stdout);
+	exit(EX_OK);
+}
+
+int print_version( void ) {
+	printf("%s Version %s\n",progname, version);
+	return TRUE;
+}
+
+int print_help( void ) {
+	time_t	t = 0;
+	char	*p;
+	char	*p2;
+
+	printf("\n");
+	printf("%s converts a unix timestamp into a human readable date.\n", 
+		progname);
+	printf("\n");
+	printf("Usage: unixtime [-h, --help] [-V, --version] <TIMESTAMP>\n");
+	printf("\n");
+	printf("Where <TIMESTAMP> is the number of seconds since the Epoch\n");
+	if((p = strdup(ctime(& t))) != NULL) {
+		/* ctime() return the date as string with an appended new line.
+		 * Since we do not want the new line to be printed, we terminate
+		 * the string at the position of the new line. */
+		if((p2 = strstr(p, "\n")) != NULL)
+			strcpy(p2, "\0");
+		printf("(i.e. %s).\n", p);
+		free(p);
+	}
+	printf("\n");
+
+	return TRUE;
+}