Problem
I am implementing a basic shell in C and am confused on how to best represent a list of commands where each command might be multiple commands that are run in parallel. For example, parsing the below batch file:
ls -l directory
cat README.md & du -sh directory
exit
would produce a data structure like such:
[
[
["ls", "-l", "directory"],
],
[
["cat", "README.md"],
["du", "-sh", "directory"],
],
[
["exit"],
],
]
In particular, I am struggling to determine the most convenient data structure(s) to use as arguments to my exec_many function.
int exec_many(/* list of list of list of strings /*) {
...
}
I am willing to implement a subset of vector if that is necessary, but I assume there is a more C-like way to go about this problem.
What I’ve Tried
The only solution I’ve been able to come up with that meets the requirements is an API like such:
struct Command {
string *args;
int argc;
};
struct Commands {
Command *commands;
int count;
};
int exec_many(Commands *commands, int count) {
...
}
My issues with this solution are:
- Defining a struct for each nested layer seems tedious and unnecessary
- Constructing the structures requires full knowledge of length beforehand
4
The structure you have come up with looks fine.
Defining a struct for each nested layer seems tedious and unnecessary
Einstein is often quoted as having said: Make everything as simple as possible, but not simpler1. The complexity of a solution to a problem generally has to match the complexity of the problem it solves.
The problem you are trying to model involves a tree of entities; therefore, the solution must involve representing a tree of entities.
As a matter of fact, if the solution did not involve a tree, then I would frown.
Constructing the structures requires full knowledge of length beforehand
I would suggest that it is fine that it requires full knowledge of length beforehand, but if you really do not want that, then things will get significantly more complicated: what you actually need is a tree which consists of linked lists.
With a linked list, you can keep adding nodes until you have no more nodes to add. When processing the list, you keep processing nodes until there are no more nodes.
1 Einstein did not say exactly that; he said a more convoluted thing, which can be summarized, and generalized, by paraphrasing it like that. The summarized phrase has come to be known as Einstein’s Razor. See Wikiquote: Albert Einstein, see Wikipedia: Philosophical razor, and see Quote investigator: Everything Should Be Made as Simple as Possible, But Not Simpler