Creating a Binary Project
$ cargo new --bin catsay
$ cargo run


1. Reading Command-Line Arguments with std::env::args
Listing 2-2.
$ cargo run -- "Hello I'm a cat"
Hello I'm a cat
 \ 
  \ 
     /\_/\ 
	( o o ) 
	=( I )=
	
	
2. Handling Complex Arguments with StructOpt
[dependencies] 
structopt = "0.2.15"
Listing 2-3. Reading a Single Positional Argument Using StructOpt
extern crate structopt;
use structopt::StructOpt;
#[derive(StructOpt)]
$ cargo run -- --help
Listing 2-4. Configuring the Default Value and Description
struct Options{ 
    #[structopt(default_value = "Meow!")] 
    /// What does the cat say?
    message: String, 
}
$ cargo run -- --help
ARGS:
    <message> What does the cat say? [default: Meow!]
	
	
3. Adding Binary Flags (aka Switches)
Listing 2-5. Adding a Binary Flag Called --dead
#[derive(StructOpt)] 
struct Options { 
    message: String,

    #[structopt(short = "d", long = "dead")] 
	/// Make the cat appear dead 
	dead: bool,
}
$ cargo run -- --help
Listing 2-6. Showing Different Eyes Based on the Options::dead Flag


4. Printing to STDERR
Listing 2-7. Printing to STDERR When an Error Happens
$ cargo run "woof" 1> stdout.txt 2> stderr.txt
$ cat stdout.txt
$ cat stderr.txt


5. Printing with Color
[dependencies] 
// ...
colored = "1.7.0"
Listing 2-9. Using the colored Crate


6. Reading the Cat Picture from a File
Listing 2-10. Adding the catfile Option
struct Options { 
    // ...
    #[structopt(short = "f", long = "file", parse(from_os_str))] 
    /// Load the cat picture from the specified file 
	catfile:     Option<std::path::PathBuf>,
}
$ cargo run -- --help
Listing 2-11. Reading the Catfile
Listing 2-12. A Catfile


7. Better Error Handling
Listing 2-13. Pseudo-Code for an Expended Version of the ? Operator
Listing 2-14. Changing the Function Signature to Use the ? Operator
Listing 2-15. Cargo.toml for Using the failure Crate
Listing 2-16. Defining a Context on the Result Returned by read_to_string
Listing 2-17. Cargo.toml for Using the exitfailure Crate
Listing 2-18. Using exitfailure
$ cargo run -- -f no/such/file.txt

8. Piping to Other Commands
 - Piping to STDOUT Without Color
Listing 2-19. Raw Color Escaped Code
cargo run > output.txt
NO_COLOR=1 cargo run > output.txt
	
 - Accepting STDIN
Listing 2-20. Reading from STDIN
$ echo 'Grace' | target/debug/catsay-ag --stdin
$ echo 'Grace' | NO_COLOR=1 target/debug/catsay-ag --stdin

9. Integration Testing
Listing 2-21. A Basic Smoke Test
Listing 2-22. Cargo.toml for Using assert_cmd
Listing 2-23. Example Output of a Cargo Test Run
$ cargo test
Listing 2-24. Cargo.toml for Using Predicates
Listing 2-25. Check that the STDOUT Contains a Certain String
Listing 2-26. Check that a Bad Argument Triggers a Failure