PWB1/usr/man/man1/diff.1

.th DIFF I 5/31/77
.sh NAME
diff \*- differential file comparator
.sh SYNOPSIS
.bd diff
[
.bd \-efb
] name1 name2
.sh DESCRIPTION
.it Diff
tells what lines must be changed in two files to bring them
into agreement.
If
.it"name1 (name2)"
is `\-', the standard input is used.
If
.it"name1 (name2)"
is a directory, then a file in that directory
whose file-name is the same as the file-name of 
.it "name2 (name1)"
is used.
The normal output contains lines of these forms:
.s3
.lp +5 0
.it n1
a
.it n3,n4
.br
.it n1,n2
d
.it n3
.br
.it n1,n2
c
.it n3,n4
.s3
.i0
These lines resemble
.it ed
commands to convert file
.it name1
into file
.it name2.
The numbers after the letters pertain to file
.it name2.
In fact, by exchanging `a' for `d' and reading backward
one may ascertain equally how to convert file 
.it name2
into
.it name1.
As in 
.it ed,
identical pairs where
.it n1
=
.it n2
or
.it n3
=
.it n4
are abbreviated as a single number.
.s3
Following each of these lines come all the lines that are
affected in the first file flagged by `<', 
then all the lines that are affected in the second file
flagged by `>'.
.s3
The
.bd \-b
option causes
trailing blanks (spaces and tabs) to be ignored
and other strings of blanks to compare equal.
The
.bd \-e
option produces a script of
.it "a, c"
and 
.it d
commands for the editor
.it ed,
which will recreate file
.it name2
from file
.it name1.
The
.bd \-f
option produces a similar script,
not useful with
.it ed,
in the opposite order.
In connection with
.bd \-e,
the following shell program may help maintain
multiple versions of a file.
Only an ancestral file ($1) and a chain of 
version-to-version
.it ed
scripts ($2,$3,...) made by
.it diff
need be on hand.
A `latest version' appears on
the standard output.
.s3
.lp +5 0
(cat $2 ... $9; echo \*'1,$p\*') \*v ed \*- $1
.s3
.i0
Except for occasional `jackpots',
.it diff
finds a smallest sufficient set of file
differences.
.sh FILES
/tmp/d?????
.sh "SEE ALSO"
cmp(I), comm(I), ed(I), uniq(I)
.sh DIAGNOSTICS
`jackpot' \- To speed things up, the program uses hashing.
You have stumbled on a case where there is a chance that
this has resulted in
a difference being called where none actually existed.
Sometimes reversing the order of files will make a
jackpot go away.
.sh BUGS
Editing scripts produced under the
\fB\-e\fR or
\fB\-f\fR options are naive about
creating lines consisting of a single `\fB.\fR'.