.TH DIFF 1 
.SH NAME
diff \- differential file comparator
.SH SYNOPSIS
.B diff
[
.B \-efbh
] file1 file2
.SH DESCRIPTION
.I Diff
tells what lines must be changed in two files to bring them
into agreement.
If
.I file1
.RI ( file2 )
is `\-', the standard input is used.
If
.I file1
.RI ( file2 )
is a directory, then a file in that directory
whose file-name is the same as the file-name of 
.I file2
.RI ( file1 )
is used.
The normal output contains lines of these forms:
.IP "" 5
.I n1
a
.I n3,n4
.br
.I n1,n2
d
.I n3
.br
.I n1,n2
c
.I n3,n4
.PP
These lines resemble
.I ed
commands to convert
.I file1
into
.IR file2 .
The numbers after the letters pertain to
.IR file2 .
In fact, by exchanging `a' for `d' and reading backward
one may ascertain equally how to convert 
.I file2
into
.IR file1 .
As in 
.I ed,
identical pairs where
.I n1
=
.I n2
or
.I n3
=
.I n4
are abbreviated as a single number.
.PP
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 `>'.
.PP
The
.B \-b
option causes
trailing blanks (spaces and tabs) to be ignored
and other strings of blanks to compare equal.
.PP
The
.B \-e
option produces a script of
.I "a, c"
and 
.I d
commands for the editor
.I ed,
which will recreate
.I file2
from
.IR file1 .
The
.B \-f
option produces a similar script,
not useful with
.I ed,
in the opposite order.
In connection with
.BR \-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
.I ed
scripts ($2,$3,...) made by
.I diff
need be on hand.
A `latest version' appears on
the standard output.
.IP "" 5
(shift; cat $*; echo \'1,$p\') \(bv ed \- $1
.PP
Except in rare circumstances,
.I diff
finds a smallest sufficient set of file
differences.
.PP
Option
.B \-h
does a fast, half-hearted job.
It works only when changed stretches are short
and well separated,
but does work on files of unlimited length.
Options 
.B \-e
and
.B \-f
are unavailable with
.BR \-h .
.SH FILES
/tmp/d?????
.br
/usr/lib/diffh for 
.B \-h
.SH "SEE ALSO"
cmp(1), comm(1), ed(1)
.SH DIAGNOSTICS
Exit status is 0 for no differences, 1 for some, 2 for trouble.
.SH BUGS
Editing scripts produced under the
.BR \-e " or"
.BR \-f " option are naive about"
creating lines consisting of a single `\fB.\fR'.