diff.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

.TH diff 1
.SH Name
diff \- differential file comparator
.SH Syntax
\fBdiff\fP [\fIoptions\fR] \fIdir1 dir2\fR
.br
\fBdiff\fP [\fIoptions\fR] \fIfile1 file2\fR
.SH Description
.NXR "diff command"
.NXR "file" "comparing"
.NXR "directory" "comparing"
The 
.PN diff
command compares the contents of files or groups of files, 
and lists any differences it finds. When run on regular files, 
and when comparing text files that differ
during directory comparison,
.PN diff
tells what lines must be changed
in the files to bring them into agreement.
Except in rare circumstances,
.PN diff
finds a smallest sufficient set of file differences.
If neither
.I file1
nor
.I file2
is a directory, then either
can be specified as `\-', in which case the standard input is used.
If
.I file1
is a directory,
then a file in that directory whose
filename is the same as the filename of
.I file2
is used and likewise if 
.I file2
is a directory.
.PP
If both arguments are directories,
.PN diff
sorts the contents of the directories by name, and then runs the
regular file
.PN diff
algorithm on text files that are different.
Binary files that differ,
common subdirectories, and files that appear in only one directory
are listed.
.SH Options
The following options are used when comparing directories:
.IP \-l 10
Displays the output in long format.  Each text file
is piped through
.MS pr 1
to paginate it;
other differences are summarized
after all text file differences are reported.
.IP \-n
Produces a script similar to that of
.B \-e,
but in reverse order and with a count of changed lines
on each insert or delete command.
.IP \-r
Recursively checks files in common subdirectories.
.IP \-s
Displays names of files that are the same.  
.IP \-S\fIname\fR
Starts a directory in the middle beginning with the specified file.
.PP
Except for the
.B \-b, i, t, and w
options,
which may be given with any of the others,
the following formatting options are mutually exclusive:
.IP \-b 10 
Ignores trailing blanks and other
strings of blanks and treats such portions as equal.
.IP \-c
Displays three context lines with each output line.  
For backwards compatibility, \fB\-c\fIn\fR
causes \fBn\fR number of context lines.
.IP \-C\fI\ n\fR 
Displays specified number of context lines with each output line.  
With
.B \-c
or
.B \-C
the output format is modified slightly:
the output begins with identification of the files involved and
their creation dates and then each change is separated
by a line with a dozen asterisks (*).
The lines removed from
.I file1
are marked with minus sign (-); those added to
.I file2
are marked plus sign (+).  Lines that are changed from one
file to the other are marked in both files with an exclamation 
point (!).
.IP
Changes within 
.I n
context lines of each other are grouped
together in the output.  This results in output that is usually 
much easier to interpret.
.IP \-D\fIstring\fR 
Causes
.PN diff
to create a merged version of
.I file1
and
.I file2
on the standard output.  With C preprocessor controls included,  
a compilation of the result without defining \fIstring\fR is equivalent
to compiling
.I file1,
while defining
.I string
will yield
.I file2.
.IP \-e 
Writes output to an 
.PN ed 
script.  
In connection with
.BR \-e ,
the following shell program can help maintain
multiple versions of a file.
Only an ancestral file ($1) and a chain of 
version-to-version
.PN ed
scripts ($2,$3,...) made by
.PN diff
need be available.
A latest version message appears on
the standard output.
.EX
 (shift; cat $*; echo \'1,$p\') \(bv ed \- $1
.EE
If you specify 
.B \-e
when comparing directories 
the result is a 
.MS sh 1 
script for converting text files that are common 
to the two directories from their state in
.I dir1
to their state in
.I dir2.
.IP \-f 
Writes the output in reverse order to a script.  
.IP \-h 
Makes a hasty comparison.  
It works only when changed portions are short
and well separated,
but does work on files of unlimited length.
.IP \-i
Ignores the case of letters.  For example 'A' will compare 
equal to `a'.
.IP \-t
Expand tabs in output lines.  Normal or
.B \-c
output adds character(s) to the front of each line which may affect 
the indentation of the original source lines and make the 
output listing difficult to interpret.  This option will 
preserves the original indentation.
.IP \-w
Causes whitespace (blanks and tabs) to be totally ignored.  
For example, `if\ (\ a\ ==\ b\ )' will compare equal to `if(a==b)'.
.PP
There are several options for output format;
the default output format 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
.PN 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
you can tell how to convert 
.I file2
into
.IR file1 .
As in 
.PN 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 a left angle bracket (<).
Then all the lines that are affected in the second file are listed,
flagged by a right angle bracket (>).
.SH Restrictions
.NXR "diff command" "restricted"
Editing scripts produced under the
.B \-e 
or
.B \-f 
option have trouble
creating lines consisting of a single period (.).
.PP
When comparing directories with the
.B \-b, i, t, or w
options specified,
.PN diff
first compares the files as
.PN cmp
does, and then runs the
.PN diff
algorithm if they are not equal.
If the only differences are in the blank strings,
.PN diff
may report these as differences. 
.SH Diagnostics
.NXR "diff command" "diagnostics"
Exit status is 0 for no differences, 1 for some differences,and 2
if the specified file cannot be found.
.SH Files
.TP 20
.PN /tmp/d?????
.TP
.PN/usr/lib/diffh 
for 
.B \-h
.TP
.PN /bin/pr
.SH See Also
cc(1), cmp(1), comm(1), diff3(1), ed(1)