mdb I/O redirection

[Fergus Henderson]

While reviewing Tyson's recent mdb bug fix, I started thinking about
some possible alternatives for ways of telling mdb to run the program
in a different window.

Here's what I propose:

	Usage: mdb [<options>] <executable> [<arguments>]
	Options:
		-t <file-name>, --tty <file-name>
			Redirect all of the I/O for the debugger
			to the device specified by <file-name>.
			The I/O for the program being debugged
			will not be redirected.

		-w, --window
			Run the program in a new window,
			with the program's I/O going to that
			window, but with mdb's I/O going
			to the current terminal.

		-c <command>, --window-command <command>
			Specify the command used by the --window option
			for creating a new window.  The default command
			that it uses is `xterm -e'.

Comments?

--------------------

P.S. 

It would be easy to make things a lot more complicated
than that.  For completeness, I include below a description
of additional options, etc., that I considered.
I decided against providing the additional functionality
below because I didn't think it was worth the complexity.

(1) Provide the new functionality using options to mdb:

	Usage: mdb [<options>] <executable> [<arguments>]
	Options:
		--prog-in <file-name>
		--prog-out <file-name>
		--prog-err <file-name>
			Redirect standard input, standard output, or
			standard error stream (respectively) for the
			program being debugged to the file or device
			specified by <file-name>.

		--prog-tty <file-name>
			Redirect all of the standard streams for the
			program being debugged to the file or device
			specified by <file-name>.

		--mdb-in <file-name>
		--mdb-out <file-name>
		--mdb-err <file-name>
			Redirect the debugger input, the debugger output, or
			the debugger error messages (respectively) for mdb
			to the file or device specified by <file-name>.

		--mdb-tty <file-name>
			Redirect all of the I/O for the debugger
			to the file or device specified by <file-name>.

		--prog-in-window
			Run the program in a new xterm window.

		--mdb-in-window
			Run the program in a new xterm window.

		--window-command <command>
			Specify the command used by the --prog-in-window
			or --mdb-in-window options for creating a new window. 
			The default command that these options use is
			`xterm -e'.

(2) add new functionality without adding new options

	Description:
		
		mbd's I/O normally goes to and from the current
		terminal, but you can redirect it using the normal
		shell I/O redirection.

		The I/O for the program being debugged normally goes to
		and from the same streams used for mdb, but you can
		redirect it by specificing a different command name in
		the arguments to mdb.  The command specified in the
		arguments to mdb need not be the program to be
		debugged; it can be a command which _invokes_ the
		program to be debugged.  The command can for example
		open a new window and redirect the program's I/O to
		that different window.

	Examples:

		mdb xterm -e ./a.out arg1 arg2
			Run the program `a.out' in a new xterm window;
			mdb's input and output will go to the current
			terminal, but the program's input and output
			will go to the new xterm window.

		mdb sh -c './a.out </dev/tty2 >/dev/tty2 2>&1'
			Debug the program `a.out' with the program's
			I/O redirected to /dev/tty2; mdb's input and
			output will go to the current terminal.

		mdb ./a.out < infile > outfile
			Debug the program `a.out' with the input and
			output for *both* mdb and the program being
			debugged being redirected to/from the specified
			files.

		mdb sh -c './a.out <prog-in >prog-out' <mdb-in >mdb-out
			Debug the program `a.out' with the input and
			output for mdb going to/from the files `mdb-in'
			and `mdb-out' and with the program's output
			going to/from the files `prog-in' and `prog-out'.


Unfortunately, redirecting the program's output without also
redirecting mdb's output is very tricky to implement portably.
It is trivial to implement on Linux, by having mdb
pass e.g. MERCURY_OPTIONS="--mdb-stdin /proc/$$/0 ..." 
to ensure that debugger input comes from the stdin of
the mdb script process rather than the stdin of the
debuggee,  However, I think it may be infeasibly
difficult to implement on other OSs.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "Binaries may die
WWW: <http://www.cs.mu.oz.au/~fjh>  |   but source code lives forever"
PGP: finger fjh at 128.250.37.3        |     -- leaked Microsoft memo.