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What is the first flag/option in the man pages of ssh and tcpdump?

ssh -1246AaCfgKkMNnqsTtVvXxYy 

tcpdump  -AdDefIKlLnNOpqRStuUvxX 

How is it called, why is it there, what conventions are there about it, what else uses it, why do most commands don't have it...

I couldn't find anything about it, so whatever you can tell me would be appreciated.

I do know however that it prints the version I am using and in the case of tcpdump, usage options as well.

I thought that it lists all possible flags, but it doesn't, -c -C are flags for tcpdump and not in that string for example, so is -b for ssh.

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My man page for ssh starts with:

ssh [-1246AaCfGgKkMNnqsTtVvXxYy] [-b bind_address] [-c cipher_spec]...

which is the same usage guide it prints if invoked e.g. with just ssh.

The first string there is just shorthand for the numerous single-character options which don't take arguments (it's shorter than writing [-1] [-2] [-4]...). The ones that take arguments are listed separately, probably to tell you what the argument is supposed to be.

Later on, the manual mentions that -V is actually the option to have 'ssh' print its version:

 -V      Display the version number and exit.

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