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Re: curl -fRL -o zhwiki.dict.yaml -z zhwiki.dict.yaml 1/zhwiki-20201120.dict.yaml

From: Daniel Stenberg via curl-users <>
Date: Tue, 8 Dec 2020 10:59:36 +0100 (CET)

On Tue, 8 Dec 2020, Hongyi Zhao via curl-users wrote:

> $ curl -fRL -o zhwiki.dict.yaml -z zhwiki.dict.yaml
> Even I've inspected for the manual of curl, I'm still confused on the usage
> of the options -R/-z here. Any hints will be highly appreciated.

-R is the short form of --remote-time. It makes sure the saved file gets the
same time as the remote one. As the man page says:

   This will make curl attempt to figure out the timestamp of the remote file,
   and if that is available make the local file get that same timestamp.

-z is the short form of --time-zond. It introduces a "time condition" in the
request which will ask the HTTP server to only return a contents if the remote
resource is newer than the given timestamp.

And since the -z flag gets a file name, curl will use the time stamp from that
file in the the time condition.

Conclusion: this is setup to make sure you only get a new download if the file
has been updated remotely and make sure the local file gets the same time
stamp as that remote version.

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Received on 2020-12-08