diff marker

[utzoo!henry]

Here is the source (shell script) and manual page for a program that
puts change bars in the margin of a revised version of a document.
The idea is that of PWB's diffmark, but the user interface and
implementation are different.  This is not Bell code, it carries no
nondisclosure restrictions, it may be used on any system.

The sed script possibly could be simpler, but this one works.
---------
	PATH=/bin:/usr/bin ; export PATH
	case $#
	in
		2)
		;;
	
		*)
		echo 'Usage: diffmk file1 file2' >&2
		exit 2
		;;
	esac
	
	ab=${ab-'.mc |'}
	ae=${ae-'.mc'}
	cb=${cb-'.mc |'}
	ce=${ce-'.mc'}
	db=${db-'.mc *'}
	de=${de-'.mc'}
	
	(
	diff -e $1 $2 | sed "
		/d/{	s//c/p
			a\\
	$db\\
	$de\\
	.
		d
		}
		/a/{	a\\
	$ab
			: ascan
			n
			t aclear
			: aclear
			s/^\\.\$/./
			t aend
			b ascan
			: aend
			i\\
	$ae
		}
		/c/{	a\\
	$cb
			: cscan
			n
			t cclear
			: cclear
			s/^\\.\$/./
			t cend
			b cscan
			: cend
			i\\
	$ce
		}
		"
	echo '1,$p'
	) | ed - $1
---------
.TH DIFFMK 1 local
.DA 2 March 1982
.SH NAME
diffmk \- mark differences between files
.SH SYNOPSIS
.B diffmk
file1 file2
.SH DESCRIPTION
.I Diffmk
compares two versions of a file and outputs a variant of the second
version that contains ``change mark'' commands
.RB ( .mc
for
.I nroff
or
.IR troff )
that mark the differences from the first version.
When the result is formatted, changed or inserted text is shown
by
.B |
at the right margin of each line.
The position of deleted text is shown by a single
.BR * .
.PP
If it is desired to change the formatting commands inserted by
.IR diffmk ,
the environment variables
.BR ab ,
.BR ae ,
.BR cb ,
.BR ce ,
.BR db ,
and
.BR de
can be used to specify the lines desired at the beginnings and ends
of added text, changes, and deletions respectively.
.PP
Getting a
.I diffmk
listing of (say) a C program is a bit more involved, but something
like this should work about right:
.PP
.RS
.nf
(
	echo ".pl 1"
	echo ".ll 77"
	echo ".nf"
	echo ".eo"
	diffmk file1 file2
) | nroff
.fi
.RE
.PP
The
.B .ll
setting might be altered for different programs.
.SH SEE ALSO
diff(1), troff(1)
.SH HISTORY
Local product, written somewhat in imitation of
the PWB
.IR diffmark .
.SH BUGS
Some manual tinkering may be needed to maximize output beauty.
Specifically,
file differences involving only formatting requests may produce
spurious change bars.
.PP
Shell metacharacters like
.B \e
and
.B $
must be used with care in user-specified marker lines.