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(diff.info)Comparing Directories

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Comparing Directories
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   You can use `diff' to compare some or all of the files in two
directory trees.  When both file name arguments to `diff' are
directories, it compares each file that is contained in both
directories, examining file names in alphabetical order.  Normally
`diff' is silent about pairs of files that contain no differences, but
if you use the `-s' or `--report-identical-files' option, it reports
pairs of identical files.  Normally `diff' reports subdirectories
common to both directories without comparing subdirectories' files, but
if you use the `-r' or `--recursive' option, it compares every
corresponding pair of files in the directory trees, as many levels deep
as they go.

   For file names that are in only one of the directories, `diff'
normally does not show the contents of the file that exists; it reports
only that the file exists in that directory and not in the other.  You
can make `diff' act as though the file existed but was empty in the
other directory, so that it outputs the entire contents of the file that
actually exists.  (It is output as either an insertion or a deletion,
depending on whether it is in the first or the second directory given.)
To do this, use the `-N' or `--new-file' option.

   If the older directory contains one or more large files that are not
in the newer directory, you can make the patch smaller by using the
`-P' or `--unidirectional-new-file' option instead of `-N'.  This
option is like `-N' except that it only inserts the contents of files
that appear in the second directory but not the first (that is, files
that were added).  At the top of the patch, write instructions for the
user applying the patch to remove the files that were deleted before
applying the patch.  Note: Making Patches, for more discussion of
making patches for distribution.

   To ignore some files while comparing directories, use the `-x
PATTERN' or `--exclude=PATTERN' option.  This option ignores any files
or subdirectories whose base names match the shell pattern PATTERN.
Unlike in the shell, a period at the start of the base of a file name
matches a wildcard at the start of a pattern.  You should enclose
PATTERN in quotes so that the shell does not expand it.  For example,
the option `-x '*.[ao]'' ignores any file whose name ends with `.a' or
`.o'.

   This option accumulates if you specify it more than once.  For
example, using the options `-x 'RCS' -x '*,v'' ignores any file or
subdirectory whose base name is `RCS' or ends with `,v'.

   If you need to give this option many times, you can instead put the
patterns in a file, one pattern per line, and use the `-X FILE' or
`--exclude-from=FILE' option.

   If you have been comparing two directories and stopped partway
through, later you might want to continue where you left off.  You can
do this by using the `-S FILE' or `--starting-file=FILE' option.  This
compares only the file FILE and all alphabetically later files in the
topmost directory level.