Manual should mention that check (-c) can be combined with hash option (--md5) for faster speed about rhash HOT 3 CLOSED

You are right, it should be mentioned :)

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Why can't it just look at the file extension? If a file has an extension like sha256 then it's pretty safe to assume it's not going to have md5 hashes, and if it does the person that generated the file is an idiot.

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Hash algorithm detection by file extension is implemented by 53d3366.

Also manual is updated by b0f0617:

If the hash algorithm is not specified by command line options
then RHash tries to detect algorithm from the extension of the hash file.
If detection fails, then all hash function of the same hash length are calculated,
and that significally slows down files verification. To speed up verification,
in such case, explicitly specify the hash algorithm in the command line.

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