Inter-process Communication:Pipes

We use the term pipe to mean connecting a data flow from one process to another.

Perhaps the simplest way of passing data between two programs is with the popen and pclose functions:

#include <stdio.h>
FILE *popen(const char *command, const char *open_mode);
int pclose(FILE *stream_to_close);

Captureing output from an external program:

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(){
	FILE *read_fp;
	char buffer[BUFSIZ + 1];
	int chars_read;
	memset(buffer, '/0', sizeof(buffer));
	read_fp = popen("uname -a", "r");
	if (read_fp != NULL){
		chars_read = fread(buffer, sizeof(char), BUFSIZ, read_fp);
		if (chars_read > 0){
			printf("Output was:-/n%s/n", buffer);
		}
		pclose(read_fp);
		exit(EXIT_SUCCESS);
	}
	exit(EXIT_FAILURE);
}	

Sending output to an external program:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int main(){
	FILE *write_fp;
	char buffer[BUFSIZ + 1];
	sprintf(buffer, "Once upon a time, there was.../n");
	write_fp = popen("od -c", "w");
	if (write_fp != NULL){
		//fprintf(write_fp, "Once upon a time.../n");
		fwrite(buffer, sizeof(char), strlen(buffer), write_fp);
		pclose(write_fp);
		exit(EXIT_SUCCESS);
	}
	exit(EXIT_FAILURE);
}