wget: Time-Stamping
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1 5 Time-Stamping
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1 One of the most important aspects of mirroring information from the
1 Internet is updating your archives.
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1 Downloading the whole archive again and again, just to replace a few
1 changed files is expensive, both in terms of wasted bandwidth and money,
1 and the time to do the update. This is why all the mirroring tools
1 offer the option of incremental updating.
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1 Such an updating mechanism means that the remote server is scanned in
1 search of “new” files. Only those new files will be downloaded in the
1 place of the old ones.
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1 A file is considered new if one of these two conditions are met:
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1 1. A file of that name does not already exist locally.
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1 2. A file of that name does exist, but the remote file was modified
1 more recently than the local file.
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1 To implement this, the program needs to be aware of the time of last
1 modification of both local and remote files. We call this information
1 the “time-stamp” of a file.
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1 The time-stamping in GNU Wget is turned on using ‘--timestamping’
1 (‘-N’) option, or through ‘timestamping = on’ directive in ‘.wgetrc’.
1 With this option, for each file it intends to download, Wget will check
1 whether a local file of the same name exists. If it does, and the
1 remote file is not newer, Wget will not download it.
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1 If the local file does not exist, or the sizes of the files do not
1 match, Wget will download the remote file no matter what the time-stamps
1 say.
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