feat: Add Environment Variable module (#409)

src/module.rs

@@ -12,6 +12,7 @@ pub const ALL_MODULES: &[&str] = &[
     "character",
     "cmd_duration",
     "directory",
+    "env_var",
     "git_branch",
     "git_state",
     "git_status",

src/modules/env_var.rs

@@ -0,0 +1,43 @@
+use ansi_term::Color;
+use std::env;
+
+use super::{Context, Module};
+
+/// Creates a module with the value of the chosen environment variable
+///
+/// Will display the environment variable's value if all of the following criteria are met:
+///     - env_var.disabled is absent or false
+///     - env_var.variable is defined
+///     - a variable named as the value of env_var.variable is defined
+pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
+    let mut module = context.new_module("env_var");
+    let module_style = module
+        .config_value_style("style")
+        .unwrap_or_else(|| Color::Black.bold().dimmed());
+
+    let env_name = module.config_value_str("variable")?;
+
+    let default_value = module.config_value_str("default");
+
+    let env_value = get_env_value(env_name, default_value)?;
+
+    let prefix = module.config_value_str("prefix").unwrap_or("").to_owned();
+    let suffix = module.config_value_str("suffix").unwrap_or("").to_owned();
+
+    module.set_style(module_style);
+    module.get_prefix().set_value("with ");
+    module.new_segment_if_config_exists("symbol");
+    module.new_segment("env_var", &format!("{}{}{}", prefix, env_value, suffix));
+
+    Some(module)
+}
+
+fn get_env_value(name: &str, default: Option<&str>) -> Option<String> {
+    match env::var_os(name) {
+        Some(os_value) => match os_value.into_string() {
+            Ok(value) => Some(value),
+            Err(_error) => None,
+        },
+        None => default.map(|value| value.to_owned()),
+    }
+}

src/modules/mod.rs

@@ -3,6 +3,7 @@ mod aws;
 mod character;
 mod cmd_duration;
 mod directory;
+mod env_var;
 mod git_branch;
 mod git_state;
 mod git_status;
@@ -30,6 +31,7 @@ pub fn handle<'a>(module: &str, context: &'a Context) -> Option<Module<'a>> {
     match module {
         "aws" => aws::module(context),
         "directory" => directory::module(context),
+        "env_var" => env_var::module(context),
         "character" => character::module(context),
         "nodejs" => nodejs::module(context),
         "rust" => rust::module(context),

src/print.rs

@@ -15,7 +15,6 @@ const DEFAULT_PROMPT_ORDER: &[&str] = &[
     "username",
     "hostname",
     "directory",
-    "aws",
     "git_branch",
     "git_state",
     "git_status",
@@ -27,6 +26,8 @@ const DEFAULT_PROMPT_ORDER: &[&str] = &[
     "golang",
     "java",
     "nix_shell",
+    "aws",
+    "env_var",
     "cmd_duration",
     "line_break",
     "jobs",