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touch
: Change file timestamps
touch
changes the access and/or modification times of the
specified files. Synopsis:
touch [option]... file... |
On older systems, touch
supports an obsolete syntax, as follows.
If the first file would be a valid argument to the `-t'
option and no timestamp is given with any of the `-d', `-r',
or `-t' options and the `--' argument is not given, that
argument is interpreted as the time for the other files instead of
as a file name. POSIX 1003.1-2001 (see section 2.5 Standards conformance)
does not allow this; use `-t' instead.
Any file that does not exist is created empty.
If changing both the access and modification times to the current
time, touch
can change the timestamps for files that the user
running it does not own but has write permission for. Otherwise, the
user must own the files.
Although touch
provides options for changing two of the times --
the times of last access and modification -- of a file, there is actually
a third one as well: the inode change time. This is often referred to
as a file's ctime
.
The inode change time represents the time when the file's meta-information
last changed. One common example of this is when the permissions of a
file change. Changing the permissions doesn't access the file, so
the atime doesn't change, nor does it modify the file, so the mtime
doesn't change. Yet, something about the file itself has changed,
and this must be noted somewhere. This is the job of the ctime field.
This is necessary, so that, for example, a backup program can make a
fresh copy of the file, including the new permissions value.
Another operation that modifies a file's ctime without affecting
the others is renaming. In any case, it is not possible, in normal
operations, for a user to change the ctime field to a user-specified value.
The program accepts the following options. Also see 2. Common options.
touch
.
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