How to call execute command line in C++

Question

For example, I have a script ./helloworld.sh

I would like to call it in C++, how do I do that? Which library can be used?

score 10 · Accepted Answer · answered Jul 07 '10 at 21:29

10

try

system("./helloworld.sh");

answered Jul 07 '10 at 21:29

bits

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2

It's in the "" header, or "" if you like that better. – mooware Jul 07 '10 at 21:34
It should be `std::system` when you include `` - see http://stackoverflow.com/questions/2900785/ – MSalters Jul 08 '10 at 13:46

score 5 · Answer 2 · answered Jul 07 '10 at 21:37

5

If you just want to run it (and nothing else)

system("./helloworld.sh");

If you need to get the stdin/stdout then you need to use popen()

FILE*  f = popen("./helloworld.sh","r");

answered Jul 07 '10 at 21:37

Martin York

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score 3 · Answer 3 · answered Jul 07 '10 at 21:30

3

try system().

answered Jul 07 '10 at 21:30

KLee1

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score 1 · Answer 4 · answered Jul 07 '10 at 21:32

1

In C there are also the execxxx functions from unistd.h. They have a big advantage over the simple system as you can specify environment variables for your process to run in among other levels of control for the arguments management.

answered Jul 07 '10 at 21:32

jdehaan

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What would he be willing to do with an bash sh file under Windows? :-) – jdehaan Jul 07 '10 at 21:35
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You would also lose control of the c++ program wouldn't you? If I remember, exec never returns. – KLee1 Jul 07 '10 at 21:35
@KLee1, you are absolutely right, the process is replaced... Not such a good idea in cases you want to control the stuff after all. I forgot that. – jdehaan Jul 07 '10 at 21:40
IMO system is the way to go, since its platform independent, and specifying environment variables isnt a problem at all, since you can set the desired environment variables beforehand with more `system` calls (i am thinking of set/export). Btw @jdehaan, MSYS supports sh files. – smerlin Jul 07 '10 at 22:48

score 1 · Answer 5 · answered Jul 07 '10 at 22:29

There are at least two possible ways. (I suppose you are asking about Unix-like systems when using shell scripts).

The first one is very simple, but is blocking (it returns after the command has been completed):

/* Example in pure C++ */
#include <cstdlib>
int ret = std::system("/home/<user>/helloworld.sh");

/* Example in C/C++ */
#include <stdlib.h>
int ret = system("/home/<user>/helloworld.sh");

The second way is not that easy, but could be non-blocking (script can be run as parallel process):

/* Example in C/C++ */
#include <unistd.h>
pid_t fork(void);
int execv(const char *path, char *const argv[]);

/* You have to fork process first. Search for it, if you don't know how to do it.
 * In child process you have to execute shell (eg. /bin/sh) with one of these
 * exec* functions and you have to pass path-to-your-script as the argument.
 * If you want to get script output (stdout) on-the-fly, you can do that with
 * pipes. Just create the reading pipe in parent process before forking
 * the process and redirect stdout to the writing pipe in the child process.
 * Then you can just use read() function to read the output whenever you want.
 */

since the OP asked for a C++ way, you should not mention things like fork/execv... and btw, when you use fork already, there is no reason to use execv instead of execv, or is there ? — smerlin, Jul 07 '10 at 22:51

score 0 · Answer 6 · answered Jul 07 '10 at 21:36

if you also want to get the output of the script do

char fbuf[256];
char ret[2555]; 
FILE *fh;
if ((fh = popen("./helloworld.sh", "r")) == NULL) {
    return 0;
}else{
    while ( fgets(fbuf, sizeof(fbuf), fh) ) {   
     strcat(ret, fbuf);            
     }          
}
pclose(fh);

How to call execute command line in C++

6 Answers6