SysIII/usr/src/man/man1/diff.1

.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
.BR \- ,
the standard input is used.
If
.I file1\^
.RI ( file2 )
is a directory, then a file in that directory with the name
.I file2\^
.RI ( file1 )
is used.
The normal output contains lines of these forms:
.IP "" 5
.I n1\^
.B a
.I n3,n4\^
.br
.I n1,n2\^
.B d
.I n3\^
.br
.I n1,n2\^
.B 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
.B a
for
.B d
and reading backward one may ascertain equally how to convert 
.I file2\^
into
.IR file1 .
As in 
.IR 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 \f3<\fP, 
then all the lines that are affected in the second file
flagged by \f3>\fP.
.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
.IR a,
.I c\^
and 
.I d\^
commands for the editor
.IR ed ,
which will recreate
.I file2\^
from
.IR file1 .
The
.B \-f
option produces a similar script,
not useful with
.IR 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 \(fm1,$p\(fm) \(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 differences, 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 period (\fB.\fP).