running shell functions based on user input.

I want to use the system() function to change directories, and run a few programs based on user input.

Code so far:

Code:

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#include <stdio.h>


int main()
{
        int MAX_PATH = 100;
        int i;
        char path[MAX_PATH];
        char cd_cmd[MAX_PATH + 3];
        printf("Please enter sox src directory: ");
        fgets(path,MAX_PATH,stdin);
        for(i = 0; i < MAX_PATH; i++)
        {
            if(path[i] == '\n')
            {
                path[i] = '\0';
                break;
            }
        }
        cd_cmd[0] = 'c';
        cd_cmd[1] = 'd';
        cd_cmd[2] = ' ';
        for(i = 0; i < MAX_PATH; i++)
        {
                cd_cmd[i+3] = path[i];
        }
        printf("cd_cmd is now %s \n", cd_cmd);
        system("ls -l");
        system(cd_cmd);
        system("ls -l");
               
        return(0);
}

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I also tried omitting the whole cd_cmd array and doing this:

Code:

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system("cd ", path);

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that compiled, but didn't change the directory like I wanted it to.

So how do I get a path from a user and change the current directory to that?

Thanks!

chdir()

Quote:

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Originally Posted by brewbuck

chdir()

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Thank you very much. That solved it!


edit: My question still stands, though, as I now need to do other commands that involve some user input. example: ./sox chimes.wav -r 8000 -c 1 -u -1 cchimes.wav where chimes.wav and cchimes.wav are user defined.

http://faq.cprogramming.com/cgi-bin/...&id=1043284392

u can also use snprintf() function to accept command/data from the user and place that in the buffer and pass the same to the system()...this will solve the issue...otherwise u can also use exec() functions, eg. execvp() and pass the array of command and their options to get executed:)

But the exec*() family never returns. It replaces your process with the new one.

ya thats correct...the child process gets executed and the control never returns to the parent process...so depending on ur requirement u can use execvp()...if u want control back to the parent process, use snprintf() to copy the exact command in the buffer and pass that to the system():)

Or you could, on POSIX, use one of the spawn*() functions, which have the same interface as exec*(), but spawn a new process.

But if you prefix your exec() call with a fork() call, you have all the control you could ever want.

can u plz let me know how exactly to implement it, i mean prefixing exec() before fork()...if u give a code example, that wud be gr8:)

It would be great if you could drop the kiddie speak and search the board for many previous examples.

ya sure...thanx:)

ok, thanks for the help guys. Here's what I have that works now:

Code:

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snprintf(cmd, MAX_PATH+(MAX_FILE*2)+25, "%ssox %s -r 8000 -c 1 -u -1", path, file);
    snprintf(cmd, MAX_PATH+(MAX_FILE*2)+25, "%s temp%s", cmd, outfile);

    system(cmd);

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For those that are wondering, it accepts a .wav file, and converts it to 8 bit samples at 8kHz, single channel and saves in new location.

edit: Moved to general c programming, as the next part has nothing specific to Linux

Be careful to sanitize "path" if it comes from user input. As it is, it looks like a good place for command injection. (Of course, that only applies if this is somehow externally reachable. But it is something to keep in mind.)

Quote:

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Originally Posted by CornedBee

Be careful to sanitize "path" if it comes from user input. As it is, it looks like a good place for command injection. (Of course, that only applies if this is somehow externally reachable. But it is something to keep in mind.)

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I have no idea what that means :p

My very first experience with terminal was only a couple of weeks ago, and as I've got nobody around to help me out, and I'm to busy during the day to put a huge amount of effort into it I'm moving pretty slowly.