Question

For a project in C, we need to build a shell over a Unix server.

It needs to be able to execute functionality native to Unix, and not bash (or any other Unix shell).

I am writing a method in the hopes to generalize a call to a command. into a general function:

#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/wait.h> #include <string.h> #include <limits.h>  void execCmd(char* cmd,char* options) {    char directory[MAX_CANON] = '/bin/'; //currently is just set to /bin    char* toExec = strcat(directory,cmd); 

I would like to set the variable ‘directory’ to the proper directory for the Unix command I’m calling.

So, in essence, I would like to be able to use something like char directory[MAX_CANON] = which(cmd);

so that the which function will return me the directory of the command I’m trying to call.

If you feel this is not a good solution, please recommend some other way.

Thanks

EDIT: I guess at worst I could do a massive if-else statement, setting the ‘directory’ vbl based on the cmd parameter.

Answer 1

What you’re asking for is the command ‘which’, ie

me@stackoverflow:~$ which which /usr/bin/which 

On linux it’s a shell script, so take a look a gander.

However, I don’t think this is required to make a UNIX shell. If you type

man 3 exec 

you’ll find that execlp() and execvp() take care of the details of searching PATH for the given command and executing it.