Let's say here is my code:
int main() {
char *number;
system("grep total myfile > filename");
printf(number);
}
This code finds the line from myfile containing "total" and outputs it into a new file called filename. I am trying to have the output set to the char "number" directly, instead of having to write/read from filename. Is there a way to do this?
Thanks for any help!
If I understand right your title, you want get the output from the command executed,
#include <stdio.h>
#include <stdlib.h>
int main() {
char number[100];
FILE *f = popen("echo 200", "r");
while (fgets(number, 100, f) != NULL) {
printf( "%s\n", number );
}
pclose(f);
return 0;
}
Or do you simply just want to pass variable into the command AND output your variable
#include <stdio.h>
#include <stdlib.h>
int main() {
int n = 100;
char buf[100];
sprintf(buf, "echo %d > filename", n); // format the command
system(buf); // execute
printf("%d\n", n); // print the variable
return 0;
}
popen version, put your command string there, and see what the output is.> filename2 in the command, you will NOT get anything. Because outputs have been redirected to the filename2, in that case, you have to open the filename2 to get the output. You may want to remove the > filename2 from your command, get the output from the popen and process and output to filename2.The simplest way, since you're writing a file, is to open and read the file. You could do that like this:
char number[100];
FILE *fp;
system( "echo 200 > filename" );
fp = fopen( "filename", "r" );
if( fp != NULL ) {
if( fgets(number, 100, fp) != NULL ) {
printf( "%s\n", number );
}
fclose(fp);
}
If you don't want to write/read the file, you can do a little dance with forking your process, opening pipes and using exec, and reading the data straight out of the process you ran. There's bound to be a question on SO about that already.
You can use popen to start your subprocess
FILE *fp = popen("echo 200", "r");
if (fp != NULL) {
char number[20];
if (fgets(number, sizeof(number), fp))
printf("%s\n", number);
pclose(fp);
}
use sprintf() function to pre-create string with the necessary number and then just call system(your_string).
number, or do you want to read the filefilenameand set the value ofnumberaccordingly?openfilename and write it in there yourself, of course.