Adding directories to PATH

If anyone is familiar with exec maybe you could help me out. I have a basic shell that I am trying to personalize. One of the features I want to include is that when the user inputs the command PATH they are then prompted for a directory which then is cat'ed to the end of linux's PATH variable. Here is a snippet of what I have so far:

Code:

---

char *t_PATH = (char *)malloc(sizeof(char) * 100);
char c;
        if (strcmp("PATH", *g_argv) == 0)
        {
                printf("Please enter the directory you wish to add to PATH\n");
                while(c != '\n')                             
                {
                        c = getchar();
                        strncat(t_PATH, c, 1);
                }
                execve ("/bin/set PATH=$PATH:", t_PATH, "");
        }

---

It compiles fine and when I enter PATH it allows me to enter a variable but upon pressing return, I get a segmentation fault. I believe I am incorrectly using execve somehow, but I am still new to it so I am quite confused as to how to fix it.

Anyone have any ideas?

> while(c != '\n')
c isn't initialised, so who knows whether this will pass the first time around.

> strncat(t_PATH, c, 1);
- t_PATH isn't initialised, so who knows where in the string your char is appended.
- c should have been passed as &c
- strncat does NOT always append a \0, so you could still end up with a broken string.

> execve ("/bin/set PATH=$PATH:", t_PATH, "");
Variable length exec calls end with a NULL parameter, not a "" parameter.


I suppose it's worth noting that exec is the wrong thing to be calling to set the path. But you should try anyway, you'll learn something in the process.

Writing any progrem to append to the path is wrong. But that's another good thing to learn.

Here's a hint. Write a shell script that sets an environment variable, call it, and then look at the environment.
Then source the shell script instead of calling it.

Yah I could easily make a shell script to change the PATH env variable, but that is not how I want to go about doing it. I wanted to see if I would be able to change it with C code.

Essentially I was asking is there a C equivalent to:

Code:

---

PATH = PATH=$PATH:/myfolder/

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Researching more about setting environment variables in C I found this piece of code to help me out substantially:

Code:

---

 
if (-1 == putenv("PATH=/:/home/userid"))
{
      printf("putenv failed \n");
      return EXIT_FAILURE;
}

---

Why not use the setenv() function?

Quote:

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Originally Posted by cpjust

Why not use the setenv() function?

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That won't work either. Changing the parent's environment is impossible. The only way to do this is with a shell script that gets evaluated in the environment which needs to be modified.

There's no way to affect a different process's PATH.