Move --print to a subcommand

Not sure why I made it an option in the first place. A subcommand works
better for this, and keeps the interface consistent with the other
commands.

src/command.rs

@@ -6,4 +6,5 @@ pub mod known;
 pub mod list;
 pub mod main;
 pub mod run;
+pub mod show;
 pub mod uninstall;

src/command/main.rs

@@ -5,6 +5,7 @@ use crate::command::install;
 use crate::command::known;
 use crate::command::list;
 use crate::command::run as run_cmd;
+use crate::command::show;
 use crate::command::uninstall;
 use crate::config::{
     bin_directory, cache_directory, config_directory, data_directory,
@@ -30,21 +31,13 @@ Commands:
     default      Set the default version
     clean        Clean up temporary data
     implode      Removes all versions and temporary data
+    show         Prints the value of a setting.
 
 Examples:
 
     ivm install 0.8.0      # Install version 0.8.0
     ivm uninstall 0.8.0    # Uninstall version 0.8.0
-    ivm run 0.8.0 foo      # Run the command `foo` with version 0.8.0
-
-You can use the -p/--print option to display what directory ivm uses for a
-certain setting. The following settings are available:
-
-    data       The data directory
-    bin        The directory for symbolic links to executables
-    cache      The directory for storing temporary data
-    install    The directory containing all installed versions
-    config     The directory containing configuration files";
+    ivm run 0.8.0 foo      # Run the command `foo` with version 0.8.0";
 
 pub fn run() -> Result<(), Error> {
     let args: Vec<_> = env::args().collect();
@@ -53,16 +46,10 @@ pub fn run() -> Result<(), Error> {
     options.parsing_style(ParsingStyle::StopAtFirstFree);
     options.optflag("h", "help", "Shows this help message");
     options.optflag("v", "version", "Prints the version number");
-    options.optopt(
-        "p",
-        "print",
-        "Prints the path to a directory used by ivm",
-        "KIND",
-    );
 
     let matches = options.parse(&args[1..])?;
 
-    if matches.opt_present("h") {
+    if matches.opt_present("h") || matches.free.is_empty() {
         usage!(&options, USAGE);
         return Ok(());
     }
@@ -72,41 +59,6 @@ pub fn run() -> Result<(), Error> {
         return Ok(());
     }
 
-    match matches.opt_str("p").as_ref().map(|s| s.as_str()) {
-        Some("data") => {
-            println!("{}", data_directory()?.to_string_lossy());
-            return Ok(());
-        }
-        Some("bin") => {
-            println!("{}", bin_directory()?.to_string_lossy());
-            return Ok(());
-        }
-        Some("cache") => {
-            println!("{}", cache_directory()?.to_string_lossy());
-            return Ok(());
-        }
-        Some("install") => {
-            println!("{}", install_directory()?.to_string_lossy());
-            return Ok(());
-        }
-        Some("config") => {
-            println!("{}", config_directory()?.to_string_lossy());
-            return Ok(());
-        }
-        Some(kind) => {
-            return Err(Error::generic(format!(
-                "{} is not a valid value for --print",
-                kind
-            )));
-        }
-        _ => {}
-    }
-
-    if matches.free.is_empty() {
-        usage!(&options, USAGE);
-        return Ok(());
-    }
-
     // We create all necessary directories here so we don't have to do this
     // every time some piece of code needs these to exist.
     create_dir_all(cache_directory()?)?;
@@ -127,6 +79,7 @@ pub fn run() -> Result<(), Error> {
         Some("default") => default::run(cmd_args),
         Some("clean") => clean::run(cmd_args),
         Some("implode") => implode::run(cmd_args),
+        Some("show") => show::run(cmd_args),
         Some(command) => Err(Error::generic(format!(
             "The command {:?} is not valid",
             command

src/command/show.rs

@@ -0,0 +1,64 @@
+use crate::config::{
+    bin_directory, cache_directory, config_directory, data_directory,
+    downloads_directory, install_directory,
+};
+use crate::error::Error;
+use getopts::Options;
+
+const USAGE: &str = "ivm show [OPTIONS] [SETTING]
+
+Prints the value of a setting.
+
+Available settings:
+
+    data         The data directory
+    bin          The directory for symbolic links to executables
+    cache        The directory for storing temporary data
+    install      The directory containing all installed versions
+    config       The directory containing configuration files
+    downloads    The directory containing downloaded files";
+
+pub fn run(arguments: &[String]) -> Result<(), Error> {
+    let mut options = Options::new();
+
+    options.optflag("h", "help", "Shows this help message");
+
+    let matches = options.parse(arguments)?;
+
+    if matches.opt_present("h") {
+        usage!(&options, USAGE);
+        return Ok(());
+    }
+
+    match matches.free.get(0).map(|s| s.as_str()) {
+        Some("data") => {
+            println!("{}", data_directory()?.to_string_lossy());
+        }
+        Some("bin") => {
+            println!("{}", bin_directory()?.to_string_lossy());
+        }
+        Some("cache") => {
+            println!("{}", cache_directory()?.to_string_lossy());
+        }
+        Some("install") => {
+            println!("{}", install_directory()?.to_string_lossy());
+        }
+        Some("config") => {
+            println!("{}", config_directory()?.to_string_lossy());
+        }
+        Some("downloads") => {
+            println!("{}", downloads_directory()?.to_string_lossy());
+        }
+        Some(setting) => {
+            return Err(Error::generic(format!(
+                "The setting {} doesn't exist",
+                setting
+            )));
+        }
+        _ => {
+            return Err(Error::generic("You must specify a setting name"));
+        }
+    }
+
+    Ok(())
+}