diff(C)                         19 June 1992                         diff(C)


 Name

    diff - compare two text files

 Syntax

    diff [ -befh ] file1 file2

 Description

    The diff command tells the user what lines must be changed in two files
    to bring them into agreement.  If file1 or file2 is a dash (-), the stan-
    dard 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 num-
    bers after the letters pertain to file2.  In fact, by exchanging a for d
    and reading backward, one can find out in just the same way how to con-
    vert 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.  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 the files can be of unlimited
    length.  The -e and -f options cannot be used with the -h option.

 Files

    /tmp/d?????
    /usr/lib/diffh  (executable used when -h option is specified)

 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 dot (.).

 Standards conformance

    diff is conformant with:

    AT&T SVID Issue 2;
    and X/Open Portability Guide, Issue 3, 1989.