C execute python script via a system call

Question

I cannot figure out how I can execute a python script from my C code. I read that I can embed the python code inside C, but I want simply to launch a python script as if I execute it from command line. I tried with the following code:

char * paramsList[] = {"/bin/bash", "-c", "/usr/bin/python", "/home/mypython.py",NULL};
pid_t pid1, pid2;
int status;

pid1 = fork();
if(pid1 == -1)
{
    char err[]="First fork failed";
    die(err,strerror(errno));
}
else if(pid1 == 0)
{  
    pid2 = fork();

    if(pid2 == -1)
    {
        char err[]="Second fork failed";
        die(err,strerror(errno));
    }
    else if(pid2 == 0)
    {  
           int id = setsid();
           if(id < 0)
           {
               char err[]="Failed to become a session leader while daemonising";
            die(err,strerror(errno));
           }
           if (chdir("/") == -1)
           {
            char err[]="Failed to change working directory while daemonising";
            die(err,strerror(errno));
        }
        umask(0);

        execv("/bin/bash",paramsList); // python system call          

    }
    else
    {        
        exit(EXIT_SUCCESS);
    }
}
else
{    
    waitpid(pid1, &status, 0);
}

I don't know where the error is since if I replace the call to python script with the call to another executable, it works well. I have added at the beginning of my python script the line:

#!/usr/bin/python

What can I do?

Thank you in advance

Can you skip the bash call entirely and just call python, like this? — miku
– miku, Commented Jul 26, 2014 at 17:59

mafso · Accepted Answer · 2014-07-26 17:46:22Z

3

From the Bash man page:

-c string   If the -c option is present, then commands are read
            from string. If there are arguments after the string,
            they are assigned to the positional parameters,
            starting with $0.

E.g.

$ bash -c 'echo x $0 $1 $2' foo bar baz
x foo bar baz

You, however don’t want to assign to the positional parameters, so change your paramList to

char * paramsList[] = { "/bin/bash", "-c",
                        "/usr/bin/python /home/mypython.py", NULL };

answered Jul 26, 2014 at 17:46

mafso

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Scis · Accepted Answer · 2014-07-27 09:26:22Z

1

Using char * paramsList[] = {"/usr/bin/python", "/tmp/bla.py",NULL}; and execv("/usr/bin/python",paramsList); // python system call caused a successful invocation of the python script named bla.py

edited Jul 27, 2014 at 9:26

answered Jul 26, 2014 at 17:43

Scis

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