(diffutils.info)Comparing Directories

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4 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 as specified by the 'LC_COLLATE' locale
category.  Normally 'diff' is silent about pairs of files that contain
no differences, but if you use the '--report-identical-files' ('-s')
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.

   If only one file exists, 'diff' normally does not show its contents;
it merely reports that one file exists but the other does not.  You can
make 'diff' act as though the missing file is empty, 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 the missing file
is in the first or the second position.)  To do this, use the
'--new-file' ('-N') option.  This option affects command-line arguments
as well as files found via directory traversal; for example, 'diff -N a
b' treats 'a' as empty if 'a' does not exist but 'b' does, and similarly
'diff -N - b' treats standard input as empty if it is closed but 'b'
exists.

   If the older directory contains large files that are not in the newer
directory, you can make the patch smaller by using the
'--unidirectional-new-file' option instead of '-N'.  This option is like
'-N' except that it inserts the contents only 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
'--exclude=PATTERN' ('-x 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
'--exclude-from=FILE' ('-X FILE') option.  Trailing white space and
empty lines are ignored in the pattern file.

   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 '--starting-file=FILE' ('-S FILE') option.  This
compares only the file FILE and all alphabetically later files in the
topmost directory level.

   If two directories differ only in that file names are lower case in
one directory and upper case in the upper, 'diff' normally reports many
differences because it compares file names in a case sensitive way.
With the '--ignore-file-name-case' option, 'diff' ignores case
differences in file names, so that for example the contents of the file
'Tao' in one directory are compared to the contents of the file 'TAO' in
the other.  The '--no-ignore-file-name-case' option cancels the effect
of the '--ignore-file-name-case' option, reverting to the default
behavior.

   If an '--exclude=PATTERN' ('-x PATTERN') option, or an
'--exclude-from=FILE' ('-X FILE') option, is specified while the
'--ignore-file-name-case' option is in effect, case is ignored when
excluding file names matching the specified patterns.

   To tell 'diff' not to follow a symbolic link, use the
'--no-dereference' option.