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); }