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(wget.info)Time-Stamping Usage

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Time-Stamping Usage
===================

   The usage of time-stamping is simple.  Say you would like to
download a file so that it keeps its date of modification.

     wget -S http://www.gnu.ai.mit.edu/

   A simple `ls -l' shows that the time stamp on the local file equals
the state of the `Last-Modified' header, as returned by the server.  As
you can see, the time-stamping info is preserved locally, even without
`-N' (at least for HTTP).

   Several days later, you would like Wget to check if the remote file
has changed, and download it if it has.

     wget -N http://www.gnu.ai.mit.edu/

   Wget will ask the server for the last-modified date.  If the local
file has the same timestamp as the server, or a newer one, the remote
file will not be re-fetched.  However, if the remote file is more
recent, Wget will proceed to fetch it.

   The same goes for FTP.  For example:

     wget "ftp://ftp.ifi.uio.no/pub/emacs/gnus/*"

   (The quotes around that URL are to prevent the shell from trying to
interpret the `*'.)

   After download, a local directory listing will show that the
timestamps match those on the remote server.  Reissuing the command
with `-N' will make Wget re-fetch _only_ the files that have been
modified since the last download.

   If you wished to mirror the GNU archive every week, you would use a
command like the following, weekly:

     wget --timestamping -r ftp://ftp.gnu.org/pub/gnu/

   Note that time-stamping will only work for files for which the server
gives a timestamp.  For HTTP, this depends on getting a `Last-Modified'
header.  For FTP, this depends on getting a directory listing with
dates in a format that Wget can parse (Note: FTP Time-Stamping
Internals).