wget: FTP Time-Stamping Internals

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1 5.3 FTP Time-Stamping Internals
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1 In theory, FTP time-stamping works much the same as HTTP, only FTP has
1 no headers—time-stamps must be ferreted out of directory listings.
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1    If an FTP download is recursive or uses globbing, Wget will use the
1 FTP ‘LIST’ command to get a file listing for the directory containing
1 the desired file(s).  It will try to analyze the listing, treating it
1 like Unix ‘ls -l’ output, extracting the time-stamps.  The rest is
1 exactly the same as for HTTP.  Note that when retrieving individual
1 files from an FTP server without using globbing or recursion, listing
1 files will not be downloaded (and thus files will not be time-stamped)
1 unless ‘-N’ is specified.
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1    Assumption that every directory listing is a Unix-style listing may
1 sound extremely constraining, but in practice it is not, as many
1 non-Unix FTP servers use the Unixoid listing format because most (all?)
1 of the clients understand it.  Bear in mind that RFC959 defines no
1 standard way to get a file list, let alone the time-stamps.  We can only
1 hope that a future standard will define this.
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1    Another non-standard solution includes the use of ‘MDTM’ command that
1 is supported by some FTP servers (including the popular ‘wu-ftpd’),
1 which returns the exact time of the specified file.  Wget may support
1 this command in the future.
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