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     DIFF(1)                                                   DIFF(1)

          diff - differential file comparator

          diff [ -efbh ] file1 file2

          Diff tells what lines must be changed in two files to bring
          them into agreement.  If file1 (file2) is `-', the standard
          input is used.  If file1 (file2) is a directory, then a file
          in that directory whose file-name is the same as the file-
          name of file2 (file1) is used.  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
          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 standard output.

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

          Except in rare circumstances, diff finds a smallest suffi-
          cient set of file differences.

          Option -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 -e and -f are
          unavailable with -h.

     DIFF(1)                                                   DIFF(1)

          /usr/lib/diffh for -h

          cmp(1), comm(1), ed(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 `.'.