src/doc/book/src/ch12-00-an-io-project.md

   1 # An I/O Project: Building a Command Line Program
   2
   3 This chapter is a recap of the many skills you’ve learned so far and an
   4 exploration of a few more standard library features. We’ll build a command line
   5 tool that interacts with file and command line input/output to practice some of
   6 the Rust concepts you now have under your belt.
   7
   8 Rust’s speed, safety, single binary output, and cross-platform support make it
   9 an ideal language for creating command line tools, so for our project, we’ll
  10 make our own version of the classic command line search tool `grep`
  11 (**g**lobally search a **r**egular **e**xpression and **p**rint). In the
  12 simplest use case, `grep` searches a specified file for a specified string. To
  13 do so, `grep` takes as its arguments a filename and a string. Then it reads the
  14 file, finds lines in that file that contain the string argument, and prints
  15 those lines.
  16
  17 Along the way, we’ll show how to make our command line tool use the terminal
  18 features that many other command line tools use. We’ll read the value of an
  19 environment variable to allow the user to configure the behavior of our tool.
  20 We’ll also print error messages to the standard error console stream (`stderr`)
  21 instead of standard output (`stdout`), so, for example, the user can redirect
  22 successful output to a file while still seeing error messages onscreen.
  23
  24 One Rust community member, Andrew Gallant, has already created a fully
  25 featured, very fast version of `grep`, called `ripgrep`. By comparison, our
  26 version will be fairly simple, but this chapter will give you some of the
  27 background knowledge you need to understand a real-world project such as
  28 `ripgrep`.
  29
  30 Our `grep` project will combine a number of concepts you’ve learned so far:
  31
  32 * Organizing code (using what you learned about modules in [Chapter 7][ch7]<!--
  33   ignore -->)
  34 * Using vectors and strings (collections, [Chapter 8][ch8]<!-- ignore -->)
  35 * Handling errors ([Chapter 9][ch9]<!-- ignore -->)
  36 * Using traits and lifetimes where appropriate ([Chapter 10][ch10]<!-- ignore
  37   -->)
  38 * Writing tests ([Chapter 11][ch11]<!-- ignore -->)
  39
  40 We’ll also briefly introduce closures, iterators, and trait objects, which
  41 Chapters [13][ch13]<!-- ignore --> and [17][ch17]<!-- ignore --> will cover in
  42 detail.
  43
  44 [ch7]: ch07-00-managing-growing-projects-with-packages-crates-and-modules.html
  45 [ch8]: ch08-00-common-collections.html
  46 [ch9]: ch09-00-error-handling.html
  47 [ch10]: ch10-00-generics.html
  48 [ch11]: ch11-00-testing.html
  49 [ch13]: ch13-00-functional-features.html
  50 [ch17]: ch17-00-oop.html