usage: added env section

src/arg/usage.rs

@@ -158,6 +158,7 @@ impl fmt::Display for Opt
 	opt!("--unlimit", "-U"; * 3 "No limit to number of processes spawned at once"),
 	opt!("--completion", "-c" => "action"; "Set the default action on completion",  ["ACTIONS", "COMPLETION"], "ignore"),
 	opt!("--silent", "-s"; * 3 "Output no messages other than that of child processes"),
+	opt!("--stfu", "-S"; * 3 "Output no messages at all"),
 
 	opt!("\nChild I/O"),
 	opt!(where "Defaults for I/O redirections of children\nThese can be overwritten individually with explicit inputs."),
@@ -198,13 +199,14 @@ impl fmt::Display for Opt
     ]
 }
 
+/// The `process completion` section.
 #[inline] fn completion() -> impl Iterator<Item = Opt>
 {
     iter![
 	opt!(in "COMPLETION"),
 	opt!(where "Directives for how to handle abnormal process completion (i.e. non-zero exit codes)\nThis does not apply to `detached` processes", ["DETACHING"]),
 
-	opt!("ignore"; * 2 "Ignore process return code"),
+	opt!("ignore"; * 2 "Ignore process return code", ""),
 	opt!("supercede"; * 2 "If return code is a non-zero code, use it as the return code for the parent (this) process.\n\t\t\tIf there are multiple non-zero return codes, it is not specified which is returned"),
 	opt!("terminate"; * 2 "If return code is a non-zero code, abort all running children and return the code as this process' return code immediately"),
 	opt!("wait"; * 3 "Same as `terminate`, except waits for currently active processes to complete before aborting"),
@@ -216,10 +218,31 @@ impl fmt::Display for Opt
     ]
 }
 
-/// Get the sections as display iterators
+#[inline] fn environment() -> impl Iterator<Item = Opt>
+{
+    iter![
+	opt!(in "ENVIRONMENT"),
+	opt!(where "Some environment variables can control the behaviour of the program also"),
+
+	opt!("RUST_LOG"),
+	opt!(where "Controls the logging level of the parent process\nThese can be surpressed entirely by `--silent` or `--stfu`\nIf the var is not set, the default level is used."),
+	opt!("trace"; * 2 "The most verbose logging"),
+	opt!("debug"; * 2 "Include debug messages"),
+	opt!("info"; * 2 "Include information messages"),
+	opt!("warn"; * 2 "Only warnings and errors"),
+	opt!("error"; * 2 "Only errors"),
+	opt!("none"; * 2 "No diagnostic messages", ""),
+
+	opt!()
+    ]
+}
+
+/// Get the sections as display iterators.
+/// Each item in the iterator is intended to be written as a single line.
 pub fn sections() -> impl Iterator<Item = impl fmt::Display>
 {
     options()
 	.chain(actions())
 	.chain(completion())
+	.chain(environment())
 }