What does ${#${(S%%)string//(\%([KF1]|)\{*\}|\%[Bbkf])}} mean

I found this in the adam2 zsh prompt, and I have no idea what it means. Apparently it counts the length of the "string", but how it does that is beyond me.

${#${(S%%)string//(\%([K开发者_JAVA百科F1]|)\{*\}|\%[Bbkf])}}

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Your pattern counts the length of the string after stripping out some ANSI-style character formatting.

Approximately:

• ${# } - length

• ${ } - nested

• (S%%) - search substrings starting from the end

• // - substitute globally (in this case delete, since there's no slash later)

• ( ) - capture group

• \% - literal percent sign

• [KF1] - character list: K=begin background color, F=begin foreground color

• [Bbkf] - character list: B=begin bold, b=end bold, k=end background, f=end foreground

And then I get lost.

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I googled "zsh prompt regex", and found this. It says $# counts the length of the contents. That link also has more info than the zsh user's guide I found.