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DIFF(1)                     General Commands Manual                    DIFF(1)



NAME
       diff - display line-by-line differences between pairs of text files

SYNOPSIS
       diff [ -bitw ] [ -c [ # ] | -e | -f | -n | -h ]  filename1 filename2
       diff [ -bitw ] [ -Dstring ]  filename1 filename2
       diff  [ -bitw ] [ -c [ # ] | -e | -f | -n | -h ] [ -l ] [ -r ] [ -s ] [
       -Sname ]  directory1 directory2

DESCRIPTION
       diff is a differential file comparator.  When run on regular files, and
       when  comparing text files that differ during directory comparison (see
       the notes below on comparing directories), diff tells what  lines  must
       be  changed  in the files to bring them into agreement.  Except in rare
       circumstances, diff finds a smallest sufficient set of differences.  If
       neither  filename1 nor filename2 is a directory, either may be given as
       `-', in which case the standard input  is  used.   If  filename1  is  a
       directory,  a  file in that directory whose filename is the same as the
       filename of filename2 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(1)  commands to convert filename1 into file-
       name2.  The numbers after the letters pertain to filename2.   In  fact,
       by  exchanging  a  for d and reading backward one may ascertain equally
       how to convert filename2 into filename1.  As in ed(1), 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 `<&lt;', then all the lines that are affected  in
       the second file flagged by `>&gt;'.

       If  both  arguments  are  directories,  diff  sorts the contents of the
       directories by name, and then runs the regular  file  diff  program  as
       described  above on text files which are different.  Binary files which
       differ, common subdirectories, and  files  which  appear  in  only  one
       directory are listed.

OPTIONS
       -b     Ignore  trailing blanks (SPACE and TAB characters) and treat all
              other strings of blanks as equivalent.

       -i     Ignore the case of letters; for example, `A' will compare  equal
              to `a'.

       -t     Expand TAB characters in output lines.  Normal or -c output adds
              character(s) to the front of  each  line  which  may  alter  the
              indentation  of  the  original  source lines and make the output
              listing difficult to interpret.  This option will  preserve  the
              original source's indentation.

       -w     Ignore  all  blanks  (SPACE  and  TAB  characters); for example,
              `if ( a == b )' will compare equal to `if(a==b)'.

       The following four options are mutually exclusive:

       -c[#]  Produce a listing of differences with  lines  of  context.   The
              default is to present 3 lines of context and may be changed, (to
              10, for example), by -c10.  With -c the output format  is  modi-
              fied  slightly:   output begins with identification of the files
              involved and their creation dates, then each change is separated
              by a line with a dozen *s.  The lines removed from filename1 are
              marked with `- '; those added to  filename2  are  marked  `+  '.
              Lines which are changed from one file to the other are marked in
              both files with `! '.

              Changes which lie within  <context>  lines  of  each  other  are
              grouped  together on output.  This is a change from the previous
              `diff -c' but the resulting output is  usually  much  easier  to
              interpret.

       -e     Produce  a  script  of  a,  c, and d commands for the editor ed,
              which will recreate filename2 from filename1.

              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

              Extra commands are added to the output when  comparing  directo-
              ries  with  -e, so that the result is a sh script for converting
              text files which are common to the two  directories  from  their
              state in directory1 to their state in directory2.

       -f     Produce  a  script  similar  to  that of -e, not useful with ed,
              which is in the opposite order.

       -n     Produce a script similar to that of  -e,  but  in  the  opposite
              order and with a count of changed lines on each insert or delete
              command.

       -h     Do 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 for the second form of diff are as follows:

       -Dstring
              Create a merged version of filename1 and filename2 on the  stan-
              dard  output,  with  C  preprocessor controls included so that a
              compilation of the result without defining string is  equivalent
              to  compiling  filename1, while defining string will yield file-
              name2.

       Options when comparing directories are:

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

       -r     Apply diff recursively to common subdirectories encountered.

       -s     Report files which are the same, which are  otherwise  not  men-
              tioned.

       -Sname Start a directory diff in the middle, beginning with file name.

ENVIRONMENT
       The  environment  variables  LC_CTYPE, LANG, and LC_default control the
       character classification throughout diff.   On  entry  to  diff,  these
       environment  variables  are  checked  in the following order: LC_CTYPE,
       LANG, and LC_default.  When a valid value is found, remaining  environ-
       ment  variables for character classification are ignored.  For example,
       a new setting for LANG does not override the  current  valid  character
       classification  rules  of  LC_CTYPE.  When none of the values is valid,
       the shell character classification defaults to the POSIX.1 "C" locale.

FILES
       /tmp/d?????
       /usr/lib/diffh      for -h

SEE ALSO
       cc(1V), cmp(1), comm(1), cpp(1), diff3(1V), ed(1),  pr(1V),  locale(5),
       iso_8859_1(7)

DIAGNOSTICS
       Exit  status  is  0  for  no differences, 1 for some differences, 2 for
       trouble.

       Missing newline at end of fileX
            Indicates that the last line of file X did not have a NEWLINE.  If
            the lines are different, they will be flagged and output, although
            the output will seem to indicate they are the same.

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

       When  comparing  directories  with the -b, -w, or -i options specified,
       diff first compares the files (as in cmp(1), and then runs the  regular
       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 or case differences.

       The  -D  option  ignores  existing  preprocessor controls in the source
       files, and can generate #ifdefs's with overlapping scope.   The  output
       should be checked by hand, or run through `cc -E' (see cc(1V)) and then
       diffed with the original source files.  Discrepancies  revealed  should
       be corrected before compilation.



                                2 October 1989                         DIFF(1)