Make the backspace key work in the Unix V7 terminal

uv7patch.sh

cd /usr

ed ./src/cmd/getty.c <<'EOE'
12c
struct tchars tchars = { '\003', '\034', '\021', '\023', '\004', '\377' };
.
8,9c
#define ERASE '\177'
#define KILL '\025'
.
w
q
EOE

ed ./src/cmd/login.c <<'EOE'
46,47c
	ttyb.sg_erase = 0177;
	ttyb.sg_kill = 025;
.
w
q
EOE

ed ./sys/dev/tty.c <<'EOE'
559a
	 * DEL is just a very fancy backspace today.
	 * However, just reducing colp by one is insufficient.
	 * We need to send an actual ^H.
	 * We're taking this opportunity to also rub out the
	 * previous character.
	 */
	if (c==0177) {
		ttyoutput(010, tp);
		ttyoutput(' ', tp);
		ttyoutput(010, tp);
		return;
	}
	/*
.
w
q
EOE

ed ./sys/h/tty.h <<'EOE'
84c
#define	CINTR	003		/* ctl-c */
.
82c
#define	CKILL	025
.
80c
#define	CERASE	0177		/* default special characters */
.
w
q
EOE

uv7unpatch.sh

cd /usr

ed ./src/cmd/getty.c <<'EOE'
12c
struct tchars tchars = { '\177', '\034', '\021', '\023', '\004', '\377' };
.
8,9c
#define ERASE	'#'
#define KILL	'@'
.
w
q
EOE

ed ./src/cmd/login.c <<'EOE'
46,47c
	ttyb.sg_erase = '#';
	ttyb.sg_kill = '@';
.
w
q
EOE

ed ./sys/dev/tty.c <<'EOE'
560,572d
w
q
EOE

ed ./sys/h/tty.h <<'EOE'
84c
#define	CINTR	0177		/* DEL */
.
82c
#define	CKILL	'@'
.
80c
#define	CERASE	'#'		/* default special characters */
.
w
q
EOE

See Teaching an Almost 40-year Old UNIX about Backspace, by xorhash. I just turned his work into a script. uv7patch.sh patches the source code. uv7unpatch.sh undoes the patch.