DIFF(C)                              UNIX System V



     Name
          diff - compares two text files


     Syntax
          diff [ -befh ] 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.
          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 period
          (.).


     Standards Conformance
          diff is conformant with:
          AT&T SVID Issue 2, Select Code 307-127;
          and The X/Open Portability Guide II of January 1987.


     (printed 2/15/90)                                    DIFF(C)