popen_and_pclose.md

popen and pclose

popen and pclose are the useful API that are another form of executing a shell or a command with in the process.

The prototypes are as follows.

FILE *popen(const char *command, const char *mode);

int pclose(FILE *stream);

The popen call executes the shell command as a sub process. However, instead of waiting for the completion of the command, it returns a file pointer.

The file pointer can then be used to read or write to the stream. Meaning, a read gets the output of the command and a write sends the data to the sub process.

In case of failure, the file pointer returned will be NULL.

The pclose will then close the file pointer.

The following code sample shows the popen and pclose. You can download it in here

#include <stdio.h>

int main(void)
{
	char data[64];
	FILE *fp;

	fp = popen("ls -l", "r");
	if (!fp) {
		fprintf(stderr, "failed to open ls -l \n");
		return -1;
	}

	while (fgets(data, sizeof(data), fp)) {
		fprintf(stderr, "%s", data);
	}

	pclose(fp);

	return 0;
}