fish-shell/share/functions/man.fish

function man --description "Format and display the on-line manual pages"
    # Work around the "builtin" manpage that everything symlinks to,
    # by prepending our fish datadir to man. This also ensures that man gives fish's
    # man pages priority, without having to put fish's bin directories first in $PATH

    set -l manpath
    if set -q MANPATH
        set manpath $MANPATH
    else if command -qs manpath
        set manpath (command manpath)
    end
    # Notice local exported copy of the variable.
    set -lx MANPATH $manpath

    set -l fish_manpath (dirname $__fish_datadir)/fish/man
    if test -d "$fish_manpath" -a -n "$MANPATH"
        set MANPATH $fish_manpath:$MANPATH
        # Invoke man with this manpath, and we're done.
        command man $argv
        return
    end

    # If fish's man pages could not be found, just invoke man normally
    command man $argv
end