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DIFF(1P)		   POSIX Programmer's Manual		      DIFF(1P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       diff - compare two files

       diff [-c| -e| -f| -C n][-br] file1 file2

       The diff utility shall compare the contents  of	file1  and  file2  and
       write  to  standard output a list of changes necessary to convert file1
       into file2. This list should be minimal. No output shall be produced if
       the files are identical.

       The  diff  utility  shall  conform  to  the  Base Definitions volume of
       IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.

       The following options shall be supported:

       -b     Cause any amount of white space at the  end  of  a  line	to  be
	      treated  as a single <newline> (that is, the white-space charac‐
	      ters preceding the <newline> are ignored) and other  strings  of
	      white-space  characters,	not  including	<newline>s, to compare

       -c     Produce output in a form that provides three lines of context.

       -C n   Produce output in a form that provides n lines of context (where
	      n shall be interpreted as a positive decimal integer).

       -e     Produce  output  in a form suitable as input for the ed utility,
	      which can then be used to convert file1 into file2.

       -f     Produce output in an alternative form, similar in format to  -e,
	      but not intended to be suitable as input for the ed utility, and
	      in the opposite order.

       -r     Apply diff recursively to files and directories of the same name
	      when file1 and file2 are both directories.

       The following operands shall be supported:

       file1, file2
	      A	 pathname  of  a  file	to be compared. If either the file1 or
	      file2 operand is '-', the standard input shall be	 used  in  its

       If  both	 file1 and file2 are directories, diff shall not compare block
       special files, character special files, or FIFO special	files  to  any
       files  and  shall  not  compare	regular	 files to directories. Further
       details are as specified in Diff	 Directory  Comparison	Format	.  The
       behavior	 of  diff  on  other file types is implementation-defined when
       found in directories.

       If only one of file1 and file2 is a directory, diff shall be applied to
       the  non-directory  file	 and  the file contained in the directory file
       with a filename that is the same as the	last  component	 of  the  non-
       directory file.

       The  standard input shall be used only if one of the file1 or file2 op‐
       erands references standard input. See the INPUT FILES section.

       The input files may be of any type.

       The following environment variables shall affect the execution of diff:

       LANG   Provide a default value for the  internationalization  variables
	      that  are	 unset	or  null.  (See the Base Definitions volume of
	      IEEE Std 1003.1-2001, Section  8.2,  Internationalization	 Vari‐
	      ables  for the precedence of internationalization variables used
	      to determine the values of locale categories.)

       LC_ALL If set to a non-empty string value, override the values  of  all
	      the other internationalization variables.

	      Determine	 the  locale  for  the	interpretation of sequences of
	      bytes of text data as characters (for  example,  single-byte  as
	      opposed to multi-byte characters in arguments and input files).

	      Determine	 the  locale  that should be used to affect the format
	      and contents of diagnostic messages written  to  standard	 error
	      and informative messages written to standard output.

	      Determine the locale for affecting the format of file timestamps
	      written with the -C and -c options.

	      Determine the location of message catalogs for the processing of
	      LC_MESSAGES .

       TZ     Determine	 the  timezone	used  for  calculating file timestamps
	      written with the -C and -c options. If TZ is unset or  null,  an
	      unspecified default timezone shall be used.


   Diff Directory Comparison Format
       If  both	 file1 and file2 are directories, the following output formats
       shall be used.

       In the POSIX locale, each file that is present in  only	one  directory
       shall be reported using the following format:

	      "Only in %s: %s\n", <directory pathname>, <filename>

       In the POSIX locale, subdirectories that are common to the two directo‐
       ries may be reported with the following format:

	      "Common subdirectories: %s and %s\n", <directory1 pathname>,
		  <directory2 pathname>

       For each file common to the two directories if the two files are not to
       be compared, the following format shall be used in the POSIX locale:

	      "File %s is a %s while file %s is a %s\n", <directory1 pathname>,
		  <file type of directory1 pathname>, <directory2 pathname>,
		  <file type of directory2 pathname>

       For  each file common to the two directories, if the files are compared
       and are identical, no output shall be written. If the two files differ,
       the following format is written:

	      "diff %s %s %s\n", <diff_options>, <filename1>, <filename2>

       where <diff_options> are the options as specified on the command line.

       All directory pathnames listed in this section shall be relative to the
       original command line arguments. All other names	 of  files  listed  in
       this section shall be filenames (pathname components).

   Diff Binary Output Format
       In the POSIX locale, if one or both of the files being compared are not
       text files, an unspecified format shall be used that contains the path‐
       names of two files being compared and the string "differ" .

       If  both	 files being compared are text files, depending on the options
       specified, one of the following formats shall be used to write the dif‐

   Diff Default Output Format
       The  default  (without  -e,  -f, -c, or -C options) diff utility output
       shall contain lines of these forms:

	      "%da%d\n", <num1>, <num2>

	      "%da%d,%d\n", <num1>, <num2>, <num3>

	      "%dd%d\n", <num1>, <num2>

	      "%d,%dd%d\n", <num1>, <num2>, <num3>

	      "%dc%d\n", <num1>, <num2>

	      "%d,%dc%d\n", <num1>, <num2>, <num3>

	      "%dc%d,%d\n", <num1>, <num2>, <num3>

	      "%d,%dc%d,%d\n", <num1>, <num2>, <num3>, <num4>

       These lines resemble ed subcommands to convert file1  into  file2.  The
       line  numbers  before  the action letters shall pertain to file1; those
       after shall pertain to file2. Thus, by exchanging a for d  and  reading
       the  line in reverse order, one can also determine how to convert file2
       into file1. As in ed, identical pairs (where num1= num2)	 are  abbrevi‐
       ated as a single number.

       Following  each of these lines, diff shall write to standard output all
       lines affected in the first file using the format:

	      "< %s", <line>

       and all lines affected in the second file using the format:

	      "> %s", <line>

       If there are lines affected in both file1 and file2 (as with the c sub‐
       command),  the  changes	are  separated with a line consisting of three


   Diff -e Output Format
       With the -e option, a script shall be produced that  shall,  when  pro‐
       vided as input to ed, along with an appended w (write) command, convert
       file1 into file2. Only the  a  (append),	 c  (change),  d  (delete),  i
       (insert),  and  s  (substitute)	commands  of  ed shall be used in this
       script. Text lines, except those consisting  of	the  single  character
       period ( '.' ), shall be output as they appear in the file.

   Diff -f Output Format
       With  the -f option, an alternative format of script shall be produced.
       It is similar to that produced by -e, with the following differences:

	1. It is expressed in  reverse	sequence;  the	output	of  -e	orders
	   changes  from  the  end  of	the file to the beginning; the -f from
	   beginning to end.

	2. The command form <lines> <command-letter> used by -e	 is  reversed.
	   For example, 10c with -e would be c10 with -f.

	3. The	form  used  for	 ranges	 of line numbers is <space>-separated,
	   rather than comma-separated.

   Diff -c or -C Output Format
       With the -c or -C option, the output format shall consist  of  affected
       lines along with surrounding lines of context. The affected lines shall
       show which ones need to be deleted or changed in file1, and those added
       from  file2.  With the -c option, three lines of context, if available,
       shall be written before and after  the  affected	 lines.	 With  the  -C
       option, the user can specify how many lines of context are written. The
       exact format follows.

       The name and last modification time of each file shall be output in the
       following format:

	      "*** %s %s\n", file1, <file1 timestamp>
	      "--- %s %s\n", file2, <file2 timestamp>

       Each <file> field shall be the pathname of the corresponding file being
       compared. The pathname written for standard input is unspecified.

       In the POSIX locale, each <timestamp> field shall be equivalent to  the
       output from the following command:

	      date "+%a %b %e %T %Y"

       without	the trailing <newline>, executed at the time of last modifica‐
       tion of the corresponding file (or the current time,  if	 the  file  is
       standard input).

       Then,  the  following  output formats shall be applied for every set of

       First, a line shall be written in the following format:


       Next, the range of lines in file1 shall be  written  in	the  following
       format if the range contains two or more lines:

	      "*** %d,%d ****\n", <beginning line number>, <ending line number>

       and the following format otherwise:

	      "*** %d ****\n", <ending line number>

       The  ending  line  number  of an empty range shall be the number of the
       preceding line, or 0 if the range is at the start of the file.

       Next, the affected lines along with lines of context (unaffected lines)
       shall  be  written.  Unaffected lines shall be written in the following

	      "	 %s", <unaffected_line>

       Deleted lines shall be written as:

	      "- %s", <deleted_line>

       Changed lines shall be written as:

	      "! %s", <changed_line>

       Next, the range of lines in file2 shall be  written  in	the  following
       format if the range contains two or more lines:

	      "--- %d,%d ----\n", <beginning line number>, <ending line number>

       and the following format otherwise:

	      "--- %d ----\n", <ending line number>

       Then,  lines of context and changed lines shall be written as described
       in the previous formats. Lines added from file2 shall be written in the
       following format:

	      "+ %s", <added_line>

       The standard error shall be used only for diagnostic messages.



       The following exit values shall be returned:

	0     No differences were found.

	1     Differences were found.

       >1     An error occurred.


       The following sections are informative.

       If  lines  at  the end of a file are changed and other lines are added,
       diff output may show this as a delete and add, as a  change,  or	 as  a
       change  and  add; diff is not expected to know which happened and users
       should not care about the difference in output as long  as  it  clearly
       shows the differences between the files.

       If dir1 is a directory containing a directory named x, dir2 is a direc‐
       tory containing a directory named x, dir1/x  and	 dir2/x	 both  contain
       files named date.out, and dir2/x contains a file named y, the command:

	      diff -r dir1 dir2

       could produce output similar to:

	      Common subdirectories: dir1/x and dir2/x
	      Only in dir2/x: y
	      diff -r dir1/x/date.out dir2/x/date.out
	      < Mon Jul	 2 13:12:16 PDT 1990
	      > Tue Jun 19 21:41:39 PDT 1990

       The  -h	option was omitted because it was insufficiently specified and
       does not add to applications portability.

       Historical implementations employ algorithms that do not always produce
       a  minimum list of differences; the current language about making every
       effort is the best this volume of IEEE Std 1003.1-2001 can do, as there
       is no metric that could be employed to judge the quality of implementa‐
       tions against any and all  file	contents.  The	statement  "This  list
       should  be  minimal''  clearly  implies	that  implementations  are not
       expected to provide the following output when  comparing	 two  100-line
       files that differ in only one character on a single line:

	      all 100 lines from file1 preceded with "< "
	      all 100 lines from file2 preceded with "> "

       The "Only in" messages required when the -r option is specified are not
       used by most historical implementations if the -e option is also speci‐
       fied.  It  is required here because it provides useful information that
       must be provided to update a target  directory  hierarchy  to  match  a
       source  hierarchy.  The "Common subdirectories" messages are written by
       System V and 4.3 BSD when the -r option is specified. They are  allowed
       here  but are not required because they are reporting on something that
       is the same, not reporting a difference, and are not needed to update a
       target hierarchy.

       The  -c option, which writes output in a format using lines of context,
       has been included. The format is useful for a variety of reasons, among
       them being much improved readability and the ability to understand dif‐
       ference changes when the target file has line numbers that differ  from
       another	similar,  but  slightly	 different, copy. The patch utility is
       most valuable when working with difference listings using  the  context
       format.	 The  BSD  version of -c takes an optional argument specifying
       the amount of context. Rather than  overloading	-c  and	 breaking  the
       Utility	Syntax Guidelines for diff, the standard developers decided to
       add a separate option for specifying a context diff  with  a  specified
       amount  of  context  (  -C).  Also,  the	 format	 for context diffs was
       extended slightly in 4.3 BSD to allow multiple changes that are	within
       context	lines from each other to be merged together. The output format
       contains an additional four asterisks after the range of affected lines
       in  the	first  filename.  This	was to provide a flag for old programs
       (like old versions of patch) that only understand the old context  for‐
       mat. The version of context described here does not require that multi‐
       ple changes within context lines be merged, but it does not prohibit it
       either.	The  extension is upwards-compatible, so any vendors that wish
       to retain the old version of diff can do so by adding  the  extra  four
       asterisks  (that	 is,  utilities that currently use diff and understand
       the new merged format will also understand the old unmerged format, but
       not vice versa).

       The  substitute	command	 was  added as an additional format for the -e
       option. This was added to provide implementations with a way to fix the
       classic	"dot  alone  on	 a line" bug present in many versions of diff.
       Since many implementations have fixed this bug, the standard developers
       decided	not  to standardize broken behavior, but rather to provide the
       necessary tool for fixing the bug. One way to fix this bug is to output
       two periods whenever a lone period is needed, then terminate the append
       command with a period, and then use the substitute command  to  convert
       the two periods into one period.

       The  BSD-derived	 -r  option was added to provide a mechanism for using
       diff to compare two file system trees.  This  behavior  is  useful,  is
       standard	 practice on all BSD-derived systems, and is not easily repro‐
       ducible with the find utility.

       The requirement that diff not compare files in some circumstances, even
       though  they  have the same name, is based on the actual output of his‐
       torical implementations. The message specified here is already  in  use
       when  a	directory is being compared to a non-directory. It is extended
       here to preclude the problems arising from running into FIFOs and other
       files  that  would cause diff to hang waiting for input with no indica‐
       tion to the user that diff was hung. In	most  common  usage,  diff  -r
       should indicate differences in the file hierarchies, not the difference
       of contents of devices pointed to by the hierarchies.

       Many early implementations of diff require seekable  files.  Since  the
       System  Interfaces volume of IEEE Std 1003.1-2001 supports named pipes,
       the standard developers decided that such a restriction	was  unreason‐
       able.  Note  also that the allowed filename - almost always refers to a

       No directory search order is specified for diff. The historical	order‐
       ing  is, in fact, not optimal, in that it prints out all of the differ‐
       ences at the current level, including the statements about  all	common
       subdirectories before recursing into those subdirectories.

       The message:

	      "diff %s %s %s\n", <diff_options>, <filename1>, <filename2>

       does  not vary by locale because it is the representation of a command,
       not an English sentence.


       cmp, comm, ed, find

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the	referee document. The original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group		     2003			      DIFF(1P)

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