Linux rsync 可以在同步前验证内容吗
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Can rsync verify contents before syncing
提问by Arjunan
Can Rsync be configured to verify the contents of the file before they are being synced. I have heard about checksum, but I came to know that checksum only does a sampling. I want to transfer a file only if it is contents are changed and not timestamp, is there a way to do it with any of the rsync modes. In my scenario, say file sample.text will be created every week and I want to sync it with a remote server only if the contents of sample.text are changed, since it is created every week, the time stamp would obviously change. But I want the transfer only on a content change.
可以将 Rsync 配置为在同步之前验证文件的内容。我听说过校验和，但我开始知道校验和只进行采样。我只想在文件内容更改而不是时间戳时传输文件，有没有办法使用任何 rsync 模式来完成它。在我的场景中，假设文件 sample.text 将每周创建一次，我想仅当 sample.text 的内容发生更改时才将其与远程服务器同步，因为它每周创建一次，时间戳显然会发生变化。但我只希望在内容更改时进行传输。
采纳答案by Nthalk
Yes:
是的：
$ man rsync | grep "\--checksum"
-c, --checksum skip based on checksum, not mod-time & size
Rsync is pretty complicated. I recommend cuddle time with the man page and experimentation with test data before using it for anything remotely important.
Rsync 相当复杂。我建议在将其用于任何远程重要的事情之前，先阅读手册页并尝试使用测试数据。
Most of the time, people use rsync -ac source dest.
大多数时候，人们使用rsync -ac source dest.
$ man rsync | grep "\--archive"
-a, --archive archive mode; same as -rlptgoD (no -H)
And that -rlptgoDgarbage means: recursive(r), copy symlinks as symlinks(l), preserve permissions(p), preserve times(t), preserve group(g), preserve owner(o), preserve device files(D, super-user only), preserve special files(also part of D).
这-rlptgoD垃圾是指：递归（r），复制符号链接作为符号链接（l），保存权限（p），保存时间（t），保存组（g），维护所有者（o），保存设备文件（D只有超级用户），保存特殊文件（也是 的一部分D）。
The -cor --checksumis really what you are looking for (skip based on checksum, not mod-time & size). Your supposition that rsync only samples mtime and size is wrong.
该-c或--checksum真的是你正在寻找（跳过基于校验，不MOD-时间和大小）。您认为 rsync 仅对 mtime 和 size 进行采样的假设是错误的。
回答by Alex Howansky
See the --checksumoption on the rsync man page.
请参阅--checksumrsync 手册页上的选项。
Also, the --size-onlyoption will be a faster choice if you know for sure that a change of contents also means a change of size.
此外，--size-only如果您确定内容的更改也意味着大小的更改，则该选项将是一个更快的选择。
回答by oldbowman
Example:
例子：
#!/bin/bash
echo > diff.txt
rsync -rvcn --delete /source/ /destination/ > diff.txt
second_row=$(sed -n '2p' diff.txt)
if [ "$second_row" = "" ]; then
echo there was no change
else
echo there was change
fi
