DIFF(C) XENIX System V DIFF(C)
Name
diff - Compares two text files.
Syntax
diff [ -efbh ] file1 file2
Description
diff tells what lines must be changed in two files to bring
them into agreement. If file1 or file2 is a dash (-), the
standard input is used. If file1 or file2 is a directory,
diff uses the file in that directory that has the same name
as the file (file2 or file1 respectively) it is compared to.
For example:
diff /tmp dog
compares the file named dog, that is in the /tmp directory,
with the file dog in the current directory.
The normal output contains lines of these forms:
n1 a n3,n4
n1,n2 d n3
n1,n2 c n3,n4
These lines resemble ed commands to convert file1 into
file2. The numbers after the letters pertain to file2. In
fact, by exchanging a for d and reading backward, one may
ascertain equally how to convert file2 into file1. As in
ed, identical pairs where n1 = n2 or n3 = n4 are abbreviated
as a single number.
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 >.
The -b option causes trailing blanks (spaces and tabs) to be
ignored and other strings of blanks to compare equal.
The -e option produces a script of a, c and d commands for
the editor ed, which will recreate file2 from file1. The -f
option produces a similar script, not useful with ed, in the
opposite order. In connection with -e, the following shell
procedure helps maintain multiple versions of a file:
(shift; cat $*; echo '1,$p') | ed - $1
This works by performing a set of editing operations on an
original ancestral file. This is done by combining the
sequence of ed scripts given as all command line arguments
except the first. These scripts are presumed to have been
created with diff in the order given on the command line.
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DIFF(C) XENIX System V DIFF(C)
The set of editing operations is then piped as an editing
script to ed where all editing operations are performed on
the ancestral file given as the first argument on the
command line. The final version of the file is then printed
on the standard output. Only an ancestral file ($1) and a
chain of version-to-version ed scripts ($2,$3,...) made by
diff need be on hand.
Except in rare circumstances, diff finds the smallest
sufficient set of file differences.
The -h option does a fast, less-rigorous job. It works only
when changed stretches are short and well separated, but
also works on files of unlimited length. The -e and -f
options cannot be used with the -h option.
Files
/tmp/d?????
/usr/lib/diffh for -h
See Also
cmp(C), comm(C), ed(C)
Diagnostics
Exit status is 0 for no differences, 1 for some differences,
2 for errors.
Notes
Editing scripts produced under the -e or -f option do not
always work correctly on lines consisting of a single period
(.).
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