makeLED.c

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

#define LED3_PATH "/sys/class/leds/beaglebone:green:usr3"

void writeLED(char filename[], char value[]); //function prototypes
void removeTrigger();

int main(int argc, char* argv[]){
    if(argc!=2){
    printf("Usage is makeLEDC and one of:\n");
    printf(" on, off, flash or status\n");
    printf(" e.g. makeLED flash\n");
    return 2;
    }
    
    printf("Starting the makeLED program\n");
    printf("The current LED Path is: " LED3_PATH "\n");
    // select whether command is on, off, flash or status
    if(strcmp(argv[1],"on")==0){
        printf("Turning the LED on\n");
        removeTrigger();
        writeLED("/brightness", "1");
    }
    
    else if (strcmp(argv[1],"off")==0){
        printf("Turning the LED off\n");
        removeTrigger();
        writeLED("/brightness", "0");
    }
    
    else if (strcmp(argv[1],"flash")==0){
        printf("Flashing the LED\n");
        writeLED("/trigger", "timer");
        writeLED("/delay_on", "50");
        writeLED("/delay_off", "50");
    }
    
    else if (strcmp(argv[1],"status")==0){
        FILE* fp; // see writeLED function below for description
        char fullFileName[100];
        char line[80];
        sprintf(fullFileName, LED3_PATH "/trigger");
        fp = fopen(fullFileName, "rt"); //reading text this time
        
        while (fgets(line, 80, fp) != NULL){
            printf("%s", line);
        }
    
        fclose(fp);
    }
    
    else{
        printf("Invalid command!\n");
    }
    
    printf("Finished the makeLED Program\n");
    return 0;
    }


void writeLED(char filename[], char value[]){
    FILE* fp; // create a file pointer fp
    char fullFileName[100]; // to store the path and filename
    sprintf(fullFileName, LED3_PATH "%s", filename); // write path/name
    fp = fopen(fullFileName, "w+"); // open file for writing
    fprintf(fp, "%s", value); // send the value to the file
    fclose(fp); // close the file using the file pointer
}

void removeTrigger(){
    writeLED("/trigger", "none");
}