swab(1): add argument parsing

Makefile

@@ -104,7 +104,7 @@ build/bin/strcmp: src/strcmp.c build
 .PHONY: swab
 swab: build/bin/swab
 build/bin/swab: src/swab.rs build build/o/libsysexits.rlib
-	$(RUSTC) $(RUSTFLAGS) \
+	$(RUSTC) $(RUSTFLAGS) --extern getopt=build/o/libgetopt.rlib \
 		--extern sysexits=build/o/libsysexits.rlib \
 		-o $@ src/swab.rs
 

src/swab.rs

@@ -5,23 +5,48 @@ use std::{
 	vec::Vec
 };
 
-extern crate sysexits;
+extern crate getopt;
+use getopt::{ Opt, Parser };
 
-use sysexits::{ EX_OK, EX_OSERR };
+extern crate sysexits;
+use sysexits::{ EX_OK, EX_OSERR, EX_USAGE };
 
 fn oserr(s: &str, e: Error) -> ExitCode {
 	eprintln!("{}: {}", s, e);
 	ExitCode::from(EX_OSERR as u8)
 }
 
+fn usage(s: &str) -> ExitCode {
+	eprintln!("Usage: {} (-f) (-w [wordsize])", s);
+	ExitCode::from(EX_USAGE as u8)
+}
+
 fn main() -> ExitCode {
 	let argv = args().collect::<Vec<String>>();
 	let mut buf: Vec<u8> = Vec::new();
 	let mut input = stdin();
 	let mut output = stdout().lock();
 
-	let wordsize: usize = 2;
-	let force = false;
+	let mut opts = Parser::new(&argv, "fw:");
+	let mut force = false;
+	let mut wordsize: usize = 2;
+
+	loop {
+		match opts.next() {
+			None => break,
+			Some(opt) =>
+				match opt {
+					Ok(Opt('f', None)) => force = true,
+					Ok(Opt('w', Some(arg))) => {
+						match arg.parse::<usize>() {
+							Ok(w) if w % 2 == 0 => { wordsize = w; () },
+							_ => { return usage(&argv[0]); },
+						}
+					},
+					_ => { return usage(&argv[0]); }
+				}
+		}
+	}
 
 	buf.resize(wordsize, 0);