output redirection in Unix and C

Question

I am trying to run a script inside my C program using system() command. Inside main() , I run the script and it returns the results. How can I put the result of the script in some string and check for conditions? I know I can do it with files but was wondering if its possible to put the result into a string.

Sample would be like:

main()
{
  system("my_script_sh"); // How can I get the result of the my_script_sh
}

Answer 1

You can't use the system command for that. The best thing to do is use popen :

  FILE *stream;
  char buffer[150];    
  stream = popen("ls", "r");
  while ( fgets(buffer, 150, stream) != NULL ){
      // Copy the buffer to your output string etc.
  }

  pclose(stream);

Answer 2

使用popen()并将流读入char *缓冲区。

Answer 3

Well the easiest thing to do would be to take system("my_script_sh") out of your program and invoke the program from the shell with a pipe -- eg: my_script_sh | ./your_c_program my_script_sh | ./your_c_program and then your C program just reads from stdin (file descriptor 0).

If that is not possible, then have a look at man 3 popen . Basically, you use popen instead of system and it gives you a file handle that you can read from to get the output of the program.

Here are a few links that might be useful:

• http://pubs.opengroup.org/onlinepubs/009695399/functions/popen.html
• http://www.crasseux.com/books/ctutorial/Programming-with-pipes.html
• http://www.metalshell.com/source_code/23/Popen.html
• http://tldp.org/LDP/lpg/node12.html