CODEWITHSUNDEEP
c++
Chuck
Chuck

Reputation: 4892

How do I execute a string as a shell script in C++?

I'm writing a program that needs to be able to execute a shell script provided by the user. I've gotten it to execute a single shell command, but the scripts provided will be more complicated than that.

Googling got me as far as the following code snippet:

FILE *pipe;
char str[100];

// The python line here is just an example, this is *not* about executing
// this particular line.
pipe = popen("python -c \"print 5 * 6\" 2>&1", "r");

fgets(str, 100, pipe);
cout << "Output: " << str << endl;

pclose(pipe)

So that this point str has 30 in it. So far so good. But what if the command has carriage returns in it, as a shell script file would, something like the following:

pipe = popen("python -c \"print 5 * 6\"\nbc <<< 5 + 6 2>&1", "r");

With this my goal is that str eventually have 30\n11.

To put another way, assume I have a file with the following contents:

python -c "print 5 * 6"
bc <<< 5 + 6

The argument I'm sending to popen above is the string representation of that file. I want to, from within C++, send that string (or something similar) to bash and have it execute exactly as if I were in the shell and sourced it with . file.sh, but setting the str variable to what I would see in the shell if it were executed there, in this case, 30\n11.

Yes, I could write this to a file and work it that way, but that seems like it should be unnecessary.

I wouldn't think this was a new problem, so either I'm thinking about it in a completely wrong way or there's a library that I simply don't know about that already does this.

Upvotes: 2

Views: 1162

Answers (1)

ikh
ikh

Reputation: 10417

use bash -c.

#include <stdio.h>

int main()
{
    FILE *pipe = popen("bash -c \"echo asdf\necho 1234\" ", "r");
    char ch;
    while ((ch = fgetc(pipe)) != EOF)
        putchar(ch);
}

Output:

asdf
1234

(I've test on cygwin)

Upvotes: 1

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