Chapter 3. On the Catwalk

When you are alone / You are the cat, you are the phone / You are an animal

They Might Be Giants, “Don’t Let’s Start” (1986)

In this chapter, the challenge is to write a clone of cat, which is so named because it can concatenate many files into one file. That is, given files a, b, and c, you could execute cat a b c > all to stream all the lines from these three files and redirect them into a file called all. The program will accept a couple of different options to prefix each line with the line number.

You’ll learn how to do the following:

• Use testing-first development

• Test for the existence of a file

• Create a random string for a filename that does not exist

• Read regular files or STDIN (pronounced standard in)

• Use eprintln! to print to STDERR and format! to format a string

• Write a test that provides input on STDIN

• Define mutually exclusive arguments

• Use the enumerate method of an iterator

CAT(1) BSD General Commands Manual CAT(1) NAME cat -- concatenate and print files SYNOPSIS cat [-benstuv] [file ...] DESCRIPTION The cat utility reads files sequentially, writing them to the standard ...