9877l1.txt0000664000175400017510000001560210665621461012044 0ustar jillljeditor/* * showdate.c -- show date and time as per the command line options specified * * Written by Sandeep Sahore * * The showdate program computes and prints the date in the past, present, or future * offset from the current date according to the command line options specified. The * default output format is to display the date and time according to the "%c" format * specification of the UNIX date(1) command however this can modified by giving the * "-f" switch along with a format string. If invoked without any command line options * the program abends and displays usage. * * $Id: showdate.c,v 1.6 2002/06/18 23:04:01 ssahore Exp $ */ #include #include #include #include void ckarg(char *, char); /* check arguments given to the command-line options */ char *progname(char *); /* get the basename of the program */ char *eofarg(char *); /* find the end of argument string */ void ckfarg(char *); /* check the validity of options in the format string */ void usage(char *); /* print usage upon error */ void ckopts(int); /* abend if both "-e" and "-f" options are given */ char *prog, *cp; /* store the command name in the variable prog */ time_t limit; /* store the value when timekeeping overflows */ int main(int argc, char *argv[]) { int c, flag, epoch; struct tm *ptm; char *optarg, *farg, buf[BUFSIZ]; time_t limit, esec, stp, *tp = &stp; epoch = flag = 0; prog = *argv; esec = time(tp); ptm = localtime(tp); prog = progname(prog); if (argc == 1) /* print usage and abend if invoked without arguments */ usage(prog); limit = (~limit < 0) ? ~(~limit << (sizeof(time_t) * 8) - 1) : ~limit; while (--argc > 0 && (*++argv)[0] == '-') { /* abend if a standalone dash is encountered */ if (!*(argv[0] + 1)) usage(prog); while (c = *++argv[0]) switch (c) { /* process the date and time options alongwith their arguments */ case 'y': case 'm': case 'd': case 'h': case 'M': case 's': if (*++argv[0]) optarg = argv[0]; else optarg = *++argv, argc--; ckarg(optarg, c); if (c == 'y') ptm->tm_year += atoi(optarg); else if (c == 'm') ptm->tm_mon += atoi(optarg); else if (c == 'd') ptm->tm_mday += atoi(optarg); else if (c == 'h') ptm->tm_hour += atoi(optarg); else if (c == 'M') ptm->tm_min += atoi(optarg); else if (c == 's') ptm->tm_sec += atoi(optarg); argv[0] = eofarg(optarg); break; /* display the seconds elapsed since the UNIX epoch */ case 'e': ckopts(flag); epoch++; break; /* formatting directives to tweak the default output */ case 'f': ckopts(epoch); if (*++argv[0]) farg = argv[0]; else { if (farg = *++argv) argc--; else fprintf(stderr, "%s: argument required for option -- %c\n", prog, c), usage(prog); } ckfarg(farg); argv[0] = eofarg(farg); flag++; break; default: fprintf(stderr, "%s: illegal option -- %c\n", prog, c); usage(prog); } } /* abend if arguments are leftover */ if (argc) usage(prog); /* * after checking system limits print desired date and time */ if (mktime(ptm) < 0) fprintf(stderr, "%s: required time exceeds system limit\n", prog); else { if (flag) strftime(buf, sizeof buf, farg, ptm); else if (epoch) fprintf(stderr,"seconds since epoch %lu", mktime(ptm)); else strftime(buf, sizeof buf, "%c", ptm); printf("%s\n", buf); } return 0; } /* * check arguments supplied to each of the command line options */ void ckarg(char *optarg, char c) { char *temp = optarg; if (*optarg == '-' || *optarg == '+' || isdigit(*optarg)) ++optarg; else if (!*optarg) fprintf(stderr, "%s: argument required for option -%c\n", prog, c), usage(prog); else fprintf(stderr, "%s: error in processing argument %s\n", prog, temp), usage(prog); while (*optarg) { if (isdigit(*optarg)) ++optarg; else fprintf(stderr, "%s: error in processing argument %s\n", prog, temp), usage(prog); } } /* * check arguments given to the "-f" command line option */ void ckfarg(char *farg) { int c; while (c = *farg++) if (c == '%') if (c = *farg++) switch (c) { case 'a': case 'A': case 'b': case 'B': case 'c': case 'C': case 'd': case 'e': case 'E': case 'H': case 'I': case 'j': case 'm': case 'M': case 'n': case 'N': case 'o': case 'p': case 'R': case 'S': case 't': case 'u': case 'U': case 'V': case 'w': case 'W': case 'x': case 'X': case 'y': case 'Y': case 'Z': case '%': break; default: fprintf(stderr, "%s: bad format character - %c\n", prog, c); exit(2); } } /* * end abnormally if both "-e" and "-f" options are given */ void ckopts(int flag) { if (flag) fprintf(stderr, "%s: cannot specify both -e and -f options\n", prog), usage(prog); } /* * find the end of the argument string */ char *eofarg(char *optarg) { while(*optarg) ++optarg; return --optarg; } /* * get the basename of the program */ char *progname(char *cp) { while (*cp) ++cp; --cp; while (*cp) { if (*cp == '/') return ++cp; --cp; } return ++cp; } /* * print usage and abend if an error is encountered during processing */ void usage(char *prog) { fprintf(stderr, "usage: %s\n\t[-y [+|-]years]\n\t[-m [+|-]months]\n\t[-d [+|-]days]\n\t" "[-h [+|-]hours]\n\t[-M [+|-]minutes]\n\t[-s [+|-]seconds]\n\t[-e | -f format]\n", prog); exit(1); }