coreutils: Target directory
2.8 Target directory
====================
The ‘cp’, ‘install’, ‘ln’, and ‘mv’ commands normally treat the last
operand specially when it is a directory or a symbolic link to a
directory. For example, ‘cp source dest’ is equivalent to ‘cp source
dest/source’ if ‘dest’ is a directory. Sometimes this behavior is not
exactly what is wanted, so these commands support the following options
to allow more fine-grained control:
‘-T’
‘--no-target-directory’
Do not treat the last operand specially when it is a directory or a
symbolic link to a directory. This can help avoid race conditions
in programs that operate in a shared area. For example, when the
command ‘mv /tmp/source /tmp/dest’ succeeds, there is no guarantee
that ‘/tmp/source’ was renamed to ‘/tmp/dest’: it could have been
renamed to ‘/tmp/dest/source’ instead, if some other process
created ‘/tmp/dest’ as a directory. However, if ‘mv -T /tmp/source
/tmp/dest’ succeeds, there is no question that ‘/tmp/source’ was
renamed to ‘/tmp/dest’.
In the opposite situation, where you want the last operand to be
treated as a directory and want a diagnostic otherwise, you can use
the ‘--target-directory’ (‘-t’) option.
‘-t DIRECTORY’
‘--target-directory=DIRECTORY’
Use DIRECTORY as the directory component of each destination file
name.
The interface for most programs is that after processing options
and a finite (possibly zero) number of fixed-position arguments,
the remaining argument list is either expected to be empty, or is a
list of items (usually files) that will all be handled identically.
The ‘xargs’ program is designed to work well with this convention.
The commands in the ‘mv’-family are unusual in that they take a
variable number of arguments with a special case at the _end_
(namely, the target directory). This makes it nontrivial to
perform some operations, e.g., “move all files from here to ../d/”,
because ‘mv * ../d/’ might exhaust the argument space, and ‘ls |
xargs ...’ doesn’t have a clean way to specify an extra final
argument for each invocation of the subject command. (It can be
done by going through a shell command, but that requires more human
labor and brain power than it should.)
The ‘--target-directory’ (‘-t’) option allows the ‘cp’, ‘install’,
‘ln’, and ‘mv’ programs to be used conveniently with ‘xargs’. For
example, you can move the files from the current directory to a
sibling directory, ‘d’ like this:
ls | xargs mv -t ../d --
However, this doesn’t move files whose names begin with ‘.’. If
you use the GNU ‘find’ program, you can move those files too, with
this command:
find . -mindepth 1 -maxdepth 1 \
| xargs mv -t ../d
But both of the above approaches fail if there are no files in the
current directory, or if any file has a name containing a blank or
some other special characters. The following example removes those
limitations and requires both GNU ‘find’ and GNU ‘xargs’:
find . -mindepth 1 -maxdepth 1 -print0 \
| xargs --null --no-run-if-empty \
mv -t ../d
The ‘--target-directory’ (‘-t’) and ‘--no-target-directory’ (‘-T’)
options cannot be combined.