Calling "bash [script name]" in C

Question

I am trying to run a bash script to generate an OpenSSL certificate. I have the bash script in the same directory as my c code.

Relevant C code:

pid_t pid = fork();
if(pid > 0){
    char* arr[] = {"./generate_cert.sh", "direct"};
    int succ = execv(arr[0], arr);
    printf("succ: %d\n", succ);
    exit(1);
}else if(pid < 0){
    printf("Fork failed\n");
    exit(-1);
}

generate_cert.sh, My test bash script which I will eventually expand is:

#!/bin/bash
echo "$1"

It seems I have a permission denied with ./generate_cert.sh. I need to instead run bash generate_cert.sh. How do I do this with execv?

Possible duplicate of System call fork() and execv function, Using execv to do basic I/O, etc. — jww
– jww, Commented Oct 31, 2019 at 4:36
That is not an error. use perror("execv failed") to get the actual error. — Antti Haapala
– Antti Haapala, Commented Oct 31, 2019 at 4:37
Thank you for that tip on perror. I am indeed getting a permission denied. Is there a way to instead run bash generate_cert.sh? — C.Programming
– C.Programming, Commented Oct 31, 2019 at 4:43
If I substitute "bash generate_cert.sh" for the first argument, I get error: "no such file or directory" since I am now not pointing to the script location. — C.Programming
– C.Programming, Commented Oct 31, 2019 at 4:44

visibleman · Accepted Answer · 2019-10-31 07:15:56Z

1

According to the execv man page, the array must be terminated by a null pointer.

So something along the lines of this (untested):

  char* arr[] = {"./generate_cert.sh", "direct",NULL};
  int succ = execv(arr[0], arr);

Edit:

OP's problem turned out to be the execute bit wasn't set on the script file. Which was solved by chmod +x generate_cert.sh , however another alternative would be to make the execv call to /bin/bash instead. I.e something along the lines of.

char* arr[] = {"/bin/bash", "./generate_cert.sh", "direct",NULL};
int succ = execv(arr[0], arr);

edited Oct 31, 2019 at 7:15

answered Oct 31, 2019 at 4:34

visibleman

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3 Comments

C.Programming Over a year ago

I tried this and I am still getting the error. When I try to run ./generate_cert.sh direct in my terminal I get "-bash: ./generate_cert.sh: Permission denied". I can however run bash generate_cert.sh direct and it runs successfully. Could this be the problem?

visibleman Over a year ago

Yes that is a problem, you need chmod +x generate_cert.sh to make the script executable

C.Programming Over a year ago

That was my problem. Thank you so much.

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