mm(1): added -t for disabling truncation; mm.1: updated docs

docs/mm.1

@@ -10,7 +10,7 @@ mm \(en middleman
 .SH SYNOPSIS
 
 mm
-.RB [ -aenu ]
+.RB [ -aetu ]
 .RB [ -i\ input ]
 .RB [ -o\ output ]
 .\"
@@ -21,19 +21,19 @@ Catenate input files and write them to the start of each output file or stream.
 .SH OPTIONS
 
 .IP \fB-a\fP
-Opens subsequent outputs for appending rather than updating.
+Opens outputs for appending rather than updating.
 .IP \fB-e\fP
 Use the standard error as an output.
+.IP \fB-t\fP
+Causes outputs to be overwritten instead of being truncated.
+.IP \fB-u\fP
+Ensures neither input or output will be buffered.
 .IP \fB-i\fP\ \fIinput\fP
 Opens a path as an input. If one or more of the input files is \(lq-\(rq or if
 no inputs are specified, the standard input shall be used.
 .IP \fB-o\fP\ \fIoutput\fP
 Opens a path as an output. If one or more of the output files is \(lq-\(rq or if
 no outputs are specified, the standard output shall be used.
-.IP \fB-u\fP
-Ensures neither input or output will be buffered.
-.IP \fB-n\fP
-Causes SIGINT signals to be ignored.
 .\"
 .SH DIAGNOSTICS
 
@@ -45,10 +45,6 @@ exits with the appropriate
 .BR sysexits.h (3)
 status.
 .\"
-.SH CAVEATS
-
-Existing files are not truncated on ouput and are instead overwritten.
-.\"
 .SH RATIONALE
 
 The

src/mm.rs

@@ -34,19 +34,21 @@ use sysexits::{ EX_IOERR, EX_USAGE };
 
 fn main() -> ExitCode {
 	let argv = args().collect::<Vec<_>>();
-	let usage = format!("Usage: {} [-aeu] [-i input] [-o output]", argv[0]);
+	let usage = format!("Usage: {} [-aetu] [-i input] [-o output]", argv[0]);
 
 	let mut a = false; /* append rather than update */
 	let mut e = false; /* use stderr as an output */
+	let mut t = true;
 	let mut u = false; /* unbuffer i/o */
 	let mut ins = Vec::new(); /* initial inputs vector */
 	let mut outs = Vec::new(); /* initial outputs vector */
 
-	while let Some(opt) = argv.getopt("aei:o:u") {
+	while let Some(opt) = argv.getopt("aei:o:tu") {
 		match opt.opt() {
 			Ok("a") => a = true,
-			Ok("e") =>  e = true, 
+			Ok("e") => e = true, 
-			Ok("u") => u = true, 
+			Ok("u") => u = true,
+			Ok("t") => t = false,
 			Ok("i") => { /* add input */
 				let input = opt.arg().unwrap();
 				ins.push(input);
@@ -75,7 +77,7 @@ fn main() -> ExitCode {
 			return unsafe { File::from_raw_fd(stdin().as_raw_fd()) }; /* fd0 = stdin */
 		}
 
-		match File::options().append(a).open(file) {
+		match File::options().open(file) {
 			Ok(f) => f,
 			Err(e) => {
 				eprintln!("{}: {}", argv[0], e.strerror());
@@ -91,7 +93,7 @@ fn main() -> ExitCode {
 			return unsafe { File::from_raw_fd(stdout().as_raw_fd()) }; /* fd1 = stdout */
 		}
 
-		match File::options().append(a).open(file) {
+		match File::options().truncate(t).append(a).open(file) {
 			Ok(f) => return f,
 			Err(e) => {
 				eprintln!("{}: {}", argv[0], e.strerror());