A basic timer application. Can be used alongside other terminal commands to give them a required countdown before executing.

timer.c

/* CTimer - A dead-simple console timer by Bryn Miller.
 *
 * Recommended use case: `ctimer $TIME && other-command`
 */

#include <stdio.h>
#include <unistd.h>
#include <string.h>

int main(int argc, char** argv) {
  int m; int s;
  char values[10];

  // Get value from argument or prompt.
  if (argc > 1) {
    if (strlen(argv[1]) > 10) {
      fprintf(stderr, "Maximum value is 999999:59\n");
      return 65; // EX_DATAERR
    }
    strcpy(values, argv[1]);
  } else {
    printf("For how long? (mm:ss) > ");
    fgets(values, sizeof values, stdin);
  }

  // Check that the input is valid...
  // Empty string.
  if (values[1] == '\0') {
    fprintf(stderr, "You have to put a time in.\n");
    return 66; // EX_NOINPUT
  }
  // If not empty or just a newline, try to pull integers
  if (sscanf(values, "%u:%u", &m, &s) != 2) { // Error if both ints aren't assigned
    fprintf(stderr, "Invalid input; use \"mm:ss\" format (e.g. 4:20 for 4 minutes and 20 seconds).\n");
    return 64; // EX_USAGE
  }
  // No negative values accepted.
  if (s < 0 || m < 0) {
    fprintf(stderr, "Time cannot be less than 0.\n");
    return 65; // EX_DATAERR
  }
  // Cannot have more than 60 seconds in a minute.
  if (s > 60) {
    fprintf(stderr, "There are no more than 60 seconds in a minute.\n");
    return 65; // EX_DATAERR
  }

  // All checks passed, proceed to countdown.
  int totalSecs = m * 60 + s;
  setvbuf(stdout, NULL, _IONBF, 32); // Make sure time will display without newline char
  for (int i = totalSecs; i > 0; i--) {
    printf("\r% 2d:%02d ", i / 60, i % 60); // Follower space erases when number of digits changes.
    sleep(1);
  }
  printf("\r***TIMER DONE***\n\n");
  return 0; // EX_OK
}