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     DIFF(1)                                                   DIFF(1)

          diff - differential file comparison

          diff [ -l ] [ -r ] [ -s ] [ -cefh ] [ -b ] dir1 dir2
          diff [ -cefh ] [ -b ] file1 file2
          diff [ -Dstring ] [ -b ] file1 file2

          If both arguments are directories, diff sorts the contents
          of the directories by name, and then runs the regular file
          diff algorithm (described below) on text files which are
          different.  Binary files which differ, common subdirecto-
          ries, and files which appear in only one directory are
          listed.  Options when comparing directories are:

          -l   long output format; each text file diff is piped
               through pr(1) to paginate it, other differences are
               remembered and summarized after all text file differ-
               ences are reported.

          -r   causes application of diff recursively to common subdi-
               rectories encountered.

          -s   causes diff to report files which are the same, which
               are otherwise not mentioned.

               starts a directory diff in the middle beginning with
               file name.

          When run on regular files, and when comparing text files
          which differ during directory comparison, diff tells what
          lines must be changed in the files to bring them into agree-
          ment.  Except in rare circumstances, diff finds a smallest
          sufficient set of file differences.  If neither file1 nor
          file2 is a directory, then either may be given as `-', in
          which case the standard input is used.  If file1 is a direc-
          tory, then a file in that directory whose file-name is the
          same as the file-name of file2 is used (and vice versa).

          There are several options for output format; the default
          output format 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

     DIFF(1)                                                   DIFF(1)

          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 `>'.

          Except for -b, which may be given with any of the others,
          the following options are mutually exclusive:

          -e       producing a script of a, c and d commands for the
                   editor ed, which will recreate file2 from file1. In
                   connection with -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 ed scripts ($2,$3,...) made by diff need be
                   on hand.  A `latest version' appears on the stan-
                   dard output.

                           (shift; cat $*; echo '1,$p') | ed - $1

                   Extra commands are added to the output when compar-
                   ing directories with -e, so that the result is a
                   sh(1) script for converting text files which are
                   common to the two directories from their state in
                   dir1 to their state in dir2.

          -f       produces a script similar to that of -e, not useful
                   with ed, and in the opposite order.

          -c       produces a diff with lines of context.  The default
                   is to present 3 lines of context and may be
                   changed, e.g to 10, by -c10.  With -c the output
                   format is modified slightly: the output beginning
                   with identification of the files involved and their
                   creation dates and then each change is separated by
                   a line with a dozen *'s.  The lines removed from
                   file1 are marked with `-'; those added to file2 are
                   marked `+'.  Lines which are changed from one file
                   to the other are marked in both files with `!'.

          -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.

          -Dstring causes diff to create a merged version of file1 and
                   file2 on the standard output, with C preprocessor
                   controls included so that a compilation of the
                   result without defining string is equivalent to
                   compiling file1, while defining string will yield

     DIFF(1)                                                   DIFF(1)


          -b       causes trailing blanks (spaces and tabs) to be
                   ignored, and other strings of blanks to compare

          /usr/lib/diffh for -h

          cmp(1), cc(1), comm(1), ed(1), diff3(1), idiff(1)

          Exit status is 0 for no differences, 1 for some, 2 for trou-

          Editing scripts produced under the -e or -f option are naive
          about creating lines consisting of a single `.'.

          When comparing directories with the -b option specified,
          diff first compares the files ala cmp, and then decides to
          run the diff algorithm if they are not equal.  This may
          cause a small amount of spurious output if the files then
          turn out to be identical because the only differences are
          insignificant blank string differences.