CURL 中是否有 WGET -N 的等效函数？

Question

我想知道 CURL 是否允许您执行与 WGET -N 相同的功能 - 如果客户端上的现有文件比服务器上的文件旧，它只会下载/覆盖文件。

Answer 1

I realise this question is old now, but just in case someone else is looking for the answer, it seems that cURL can indeed acheieve similar to wget -N.

Because I was just looking for an answer to this question today, and I found elsewhere that cURL does have time condition option. If google brings you here first, as it did me, then I hope this answer might save you some time in looking. According to curl --help, there is a time-cond flag;

-z, --time-cond <time> Transfer based on a time condition

The other part I needed, in order to make it like wget -N, is to make it try and preserve the timestamp. This is with the -R option.

-R, --remote-time   Set the remote file's time on the local output

We can use these to download "$file", only in the condition when the current local "$file" timestamp is older than the server's file timestamp; we can do it in this form;

curl -R -o "$file" -z "$file" "$serverurl"

So, for example, I use it to check if there is a newer cygwin installer like this;

curl -R -o "C:\cygwin64\setup-x86_64.exe" -z "C:\cygwin64\setup-x86_64.exe" "https://www.cygwin.com/setup-x86_64.exe"

Answer 2

cURL doesn't have the same type of mirroring support that wget has built in. There is one setting in there with cURL that should make it pretty easy to implement this for yourself though with a little bit of wrapping logic. It's the --remote-time option:

 -R/--remote-time When used, this will make libcurl attempt to figure out the timestamp of the remote file, and if that is available make the local file get that same timestamp.