I want to access variable of c in system command but i do not know how to do it i tried like below but this does not works
#include<stdlib.h>
int main(){
int a=12;
system("echo $a");
}
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2 Answers
You can't do this via any kind of string interpolation such as you've tried. What you need to do is build the command string before passing it to system().
#include <stdio.h>
#include <stdlib.h>
int main() {
int a = 12;
char command[100];
sprintf(command, "echo %d", a);
system(command);
}
Comments
The system function takes a const char* argument and returns an integer value depending on the system; usually its the status code of the command after being executed.
int system (const char* command);
So to embed variables from your c program you'd have to build a command string and then pass it to system(); Apart from using sprintf() as suggested above you can use string functions such as strcat() as well to build complex commands from your C variables. For example
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
int a = 12;
char command[] = "ls";
char opt[] = " -l";
char cmd[50];
strcat(command, opt);
sprintf(cmd, " | head -n %d", a);
strcat(command, cmd);
printf("%s\n", command );
int rv = system(command);
printf("Return value : %d\n", rv);
return 0;
}
