What is the most efficient method for running programs from the /usr/bin directory in a C program? I am tasking with getting user input, and if the user input matches up with a program in bin, running the respective program.
I had the idea of throwing the names of all the bin's programs in a text file, and using a loop to iterate through each word in the file while comparing the word to the input. However, I figured that might be reinventing the wheel a bit. Are there any streamlined ways to do this?
The "classical" way of invoking a program from an existing process on any of the UNIX-like OS'es is to use one of the exec() functions. When you read about exec() most tutorials will start by explaining another function: fork(). These functions are very commonly used together, but don't get too caught up on that, because they are both useful in their own right.
To answer your question, a fairly efficient way of doing what you're after:
fork())execvp() functionfork() in step (2), and what you intend to do (if anything) after performing the task you described. execvp() will do the legwork for you, by automatically searching on your environment PATH for a filename matching the first argument. If the current environment does not have a PATH set, it will default to /bin:/usr/bin. Since the only way that a call to exec() can yield a return value is when that call failed, you might want to check the value of errno as part of step (4). In the event that the user input didn't match any executable in the environment PATH, errno will be set to ENOENT. Exactly how you do this and what additional steps might be worth taking will depend on whether or not you forked, along with any additional requirements for your program.