find all commands with wh, find by part of keyword in man page

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http://unix.stackexchange.com – I want to find all man pages for commands that begin with wh. But I do not understand why the following keyword does not work. man -f "wh" Also if I put man chmod in man page of chmod, it has the word "symbolic", so I put man -f "symbolic" but chmod command does not show up in the results. In short, how do I find/search commands or command description by inside-word contents? I know how to find a certain words after I get the man page, using / character, but I want to find all man pages with the search word. (HowTos)