求助，tar工具中的C参数的作用是什么？ - Chinaunix

6.10.1 Changing the Working Directory
To change the working directory in the middle of a list of file names, either on the command line or in a file specified using ‘--files-from’ (‘-T’), use ‘--directory’ (‘-C’). This will change the working directory to the specified directory after that point in the list.
‘--directory=directory’
‘-C directory’
Changes the working directory in the middle of a command line.
For example,
$ tar -c -f jams.tar grape prune -C food cherry
will place the files ‘grape’ and ‘prune’ from the current directory into the archive ‘jams.tar’, followed by the file ‘cherry’ from the directory ‘food’. This option is especially useful when you have several widely separated files that you want to store in the same archive.
Note that the file ‘cherry’ is recorded in the archive under the precise name ‘cherry’, not ‘food/cherry’. Thus, the archive will contain three files that all appear to have come from the same directory; if the archive is extracted with plain ‘tar --extract’, all three files will be written in the current directory.
Contrast this with the command,
$ tar -c -f jams.tar grape prune -C food red/cherry
which records the third file in the archive under the name ‘red/cherry’ so that, if the archive is extracted using ‘tar --extract’, the third file will be written in a subdirectory named ‘orange-colored’.
You can use the ‘--directory’ option to make the archive independent of the original name of the directory holding the files. The following command places the files ‘/etc/passwd’, ‘/etc/hosts’, and ‘/lib/libc.a’ into the archive ‘foo.tar’:
$ tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a
However, the names of the archive members will be exactly what they were on the command line: ‘passwd’, ‘hosts’, and ‘libc.a’. They will not appear to be related by file name to the original directories where those files were located.
Note that ‘--directory’ options are interpreted consecutively. If ‘--directory’ specifies a relative file name, it is interpreted relative to the then current directory, which might not be the same as the original current working directory of tar, due to a previous ‘--directory’ option.
When using ‘--files-from’ (see section Reading Names from a File), you can put various tar options (including ‘-C’) in the file list. Notice, however, that in this case the option and its argument may not be separated by whitespace. If you use short option, its argument must either follow the option letter immediately, without any intervening whitespace, or occupy the next line. Otherwise, if you use long option, separate its argument by an equal sign.
For instance, the file list for the above example will be:
-C/etc
passwd
hosts
--directory=/lib
libc.a
To use it, you would invoke tar as follows:
$ tar -c -f foo.tar --files-from list
The interpretation of ‘--directory’ is disabled by ‘--null’ option.

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