from https://www.raspberrypi.org/forums/viewtopic.php?t=56702&p=428473

stepper.c

#include <wiringPi.h>
#include <stdio.h>
#include <sys/time.h>
#include <stdlib.h>

/*

execute with "sudo ./turn 800 1" where 800 is number of steps and 1 is rotation direction.
This will turn a full revolution in 3.2 seconds, adjust delayMicrosenconds to speed up or slow down. Low torque motors may not be able to turn this fast. A 3 stack, NEMA 23 should be able to handle this speed if your load is not huge.

*/

int main (int argc, char *argv[]) {
    int stepPin = 12;   //Step Motor Pulse
    int dirPin = 16;    //Step Motor Direction
    int i, steps, dir;

    // Pins assigned by physical location on P1 header of the RPi.
    if (wiringPiSetupPhys() == -1) {
        exit (1);
    }

    // Initialize RPi GPIO Pins
    pinMode(stepPin, OUTPUT);
    pinMode(dirPin, OUTPUT);

    steps = atoi(argv[1]);
    dir = atoi(argv[2]);

    digitalWrite(dirPin, dir)       //direction of rotation

    for(i=0; i<steps; i++) {        //3200 steps = full revolution, 1600 = 180 degrees, 800 = 90 degrrees
        digitalWrite(stepPin, 1);
        delayMicroseconds(500);
        digitalWrite(stepPin, 0);
        delayMicroseconds(500);
    }

    return 0;
}