Is there a way to put the output of a system command (i.e. date) in a variable? (I'm working in C). There's probably a better way to do this, but I was thinking of just putting the output of 'date +%d', which outputs the day of the month, into a variable day using 'day = system("date +%d")'. That just seems to run 'date +%d' and dump it's output to the screen, and I think that day is just empty. And if you think that the whole running date to get the day thing is a bad idea, feel free to suggest better ones.

Use perl.

Seriously, you have to open up a pipe to "date +%d" which redirects date's output to a stream (for lack of knowing what the real word is - file handle?), and then you can read its output from the stream.

I've never done that in C though...

In your code, day has the exit code of date.

- taubz

I don't think there's a standard C way to do it offhand, but, the way that works for me here with FreeBSD is as follows:

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

#define BUFFLEN 1024

int main(int argc, char **argv)
{
FILE* filed;
char buff[BUFFLEN];

if(argc != 2) {
printf("Usage: %s command\n", argv[0]);
exit(1);
}

filed = popen(argv[1], "r");
if(filed == NULL) {
printf("Error running %s\n", argv[1]);
exit(1);
}

while(!feof(filed)) {
if(fgets(buff, BUFFLEN, filed) == NULL)
break;
printf("%s", buff);
}
pclose(filed);
}

bash-2.05$ ./popentest "date +%d"
22

See man popen for more information and fun!

That's a pretty standard UNIX way to do it. I bet there are analagous Windows API functions that do the trick as well.

Thanks a lot taubz, lordaerom, and Psion. Your input really was helpful.

The test program works and I was able to work the code into my program. All the code is working, but I need to make the int day have the value of buff (from lordaerom's example). buff seems to have a newline at the end, and that's causing things to go a little haywire. So, how do you make the newline go away?

taubz : if this was perl things would be a lot easier.

You could use strrchr to find the \n if it's at the end. If it is (and it always will be), just replace it with a \000. Then use atoi.

- taubz