Programming Concepts
It's time to start adding some functionality to our grep program. In the next few sections, we'll cover topics such as variables and mutability, iterators, optional values, and closures. These topics are quite extensive, and covering them in full detail is not the objective. Instead, we'll lay the foundation and share core fundamentals to help you gain enough understanding to leverage the documentation successfully. Using the provided links is highly recommended for full details and comprehension.
Grep Features
Grep is a fairly large program with numerous features. In this course, we won't be implementing all of them. Instead, we'll concentrate on a subset of features (with slight variations in behavior) that will help you learn Rust. The features we'll be implementing are:
| command line argument | description |
|---|---|
-n, --line-number | Prefix each line of output with the 1-based line number within its input file. |
-A num, --after-context=num | Print num lines of trailing context after matching lines. |
-B num, --before-context=num | Print num lines of leading context before matching lines. |
Printing Line Numbers
The first feature we're going to add to our grep program is the ability to print the line number of any lines that match our pattern. Coming from a language like C/C++, you may be inclined to handle this with a variable that we increment with each loop iteration. While this would work, it introduces some of the issues that plague languages like C and C++ (e.g., out-of-bounds indexing, integer overflow, and more). We'll demonstrate this and follow it up with a more idiomatic approach. Let's get going!