#include <stdio.h>

int main(int argc, char** argv)
{
    
    /* launch a process that will grep for the text "xes" and write its stdout to ./output */
    /* caution... if the command is not found the return will still return a FILE* */
    FILE* grep = popen("grep \"xes\" > output", "w");

    /* write text to the stdin of grep process */
    fprintf(grep, "boxes\n");
    fprintf(grep, "coins\n");
    fprintf(grep, "taxes\n");

    /* close the pipe */
    int r = pclose(grep);
    if (r)
    {
        fprintf(stdout, "error.  return code from pclose %d\n", r);
    }

    return 0;
}