When do I use cp --attributes-only
Say you have a file, file1
, that you know should have identical attributes to file2
(you know that file2
has the correct attributes).
$ stat file{1,2}
File: 'file1'
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 1fh/31d Inode: 2326956 Links: 1
Access: (0600/-rw-------) Uid: ( 1000/ chris) Gid: ( 1000/ chris)
Access: 2013-12-24 09:53:20.248720441 +0800
Modify: 2013-12-24 09:53:20.248720441 +0800
Change: 2013-12-24 09:53:31.011984772 +0800
Birth: -
File: 'file2'
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 1fh/31d Inode: 2326957 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1000/ chris) Gid: ( 1000/ chris)
Access: 2013-12-24 09:53:21.045382001 +0800
Modify: 2013-12-24 09:53:21.045382001 +0800
Change: 2013-12-24 09:53:21.045382001 +0800
Birth: -
One way to make sure that they match is to go and check file2
and manually apply the attributes:
$ chmod 644 file1
This is, however, cumbersome to automate and script. It would be easier to get the attributes from file2
and apply them to file1
programatically.
$ cp --attributes-only --preserve file2 file1
$ stat file1
File: 'file1'
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 1fh/31d Inode: 2326956 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1000/ chris) Gid: ( 1000/ chris)
Access: 2013-12-24 09:53:21.045382001 +0800
Modify: 2013-12-24 09:53:21.045382001 +0800
Change: 2013-12-24 09:57:06.320604649 +0800
Birth: -
--attributes-only
doesn't do anything by itself; it needs to be combined with other attribute preservation flags. From info cp
:
--attributes-only
Copy only the specified attributes of the source file to the
destination. If the destination already exists, do not alter its
contents. See the `--preserve' option for controlling which
attributes to copy.
--preserve
is used above, which is documented as being equivalent to --preserve=mode,ownership,timestamps
. Internally, you can think of this as "don't copy data" rather than "copy attributes only", which is why you have to pass --preserve
regardless.