如何将字符串参数传递给execve

Question

How to pass a string argument as shown in the program below?

The argument after -f should be a string in quotes. I tried to escape \\" but did not work. I also tried to use ' and \\' instead of \\" and again it did not work.

#include <stdio.h>
#include <unistd.h>


int main(void)
{

    char *args[] =
    {
        "/usr/ws/bin/tshark", "-i", "/tmp/ts_pipe", "-w",
        "/tmp/output.pcap", "-f", "\"not src host 1.1.1.1\"", "2>", 
        "/tmp/error.log", NULL
    };

    char *envp[] =
    {
        "PATH=$PATH:/usr/wireshark/bin",
        "LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/lib32",
        0
    };

    execve(args[0], &args[0], envp);
    fprintf(stderr, "Oops!\n");
    return -1;
}

Answer 1

Just because you need quotes in the shell, for example,

tshark -f "not src host 1.1.1.1"

doesn't mean you need them in exec. In fact, those quotes are telling the shell "this is one argument", so the shell will not split on spaces and will pass the string (without quotes) as one argument to the program. So, in C, you would simply:

char *args[] = { "-f", "not src host 1.1.1.1" }

and pass that to exec.

While we're at it, redirections like

2>errfile

are intercepted by the shell and not passed on to the command, so they won't work in exec. You'll have to do the dup()s yourself, or else just pass a whole shell command to the shell (which is a security no-no).

Answer 2

As explained in the comments, redirection will not work with execve , but you could try doing this:

#include <stdio.h>
#include <unistd.h>

int main(void)
{

    char *args[] =
    {
        "/bin/sh", "-c",
        "/usr/ws/bin/tshark -i /tmp/ts_pipe -w "
        "/tmp/output.pcap -f \"not src host 1.1.1.1\" 2> " 
        "/tmp/error.log", NULL
    };

    char *envp[] =
    {
        "PATH=$PATH:/usr/wireshark/bin",
        "LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/lib32",
        0
    };

    execve(args[0], &args[0], envp);
    fprintf(stderr, "Oops!\n");
    return -1;
}

You are basically launching sh shell with -c option and passing it your whole command as an option.