source: vendor/bash/3.1/examples/functions/whatis

#
# whatis -- and implementation of the 10th Edition Unix sh builtin `whatis'
#           command.
#
# usage: whatis arg [...]
#
# For each argument, whatis prints the associated value as a parameter,
# builtin, function, alias, or executable file as appropriate.  In each
# case, the value is printed in a form which would yield the same value
# if typed as input to the shell itself.
#

whatis()
{
        local wusage='usage: whatis arg [arg...]'
        local fail=0

        if [ $# -eq 0 ] ; then
                echo "$wusage"
                return 1
        fi

        for arg
        do
                case $(builtin type -type $arg 2>/dev/null) in
                "alias")
                        builtin alias "$arg"
                        ;;
                "function")
                        builtin type "$arg" | sed 1d
                        ;;
                "builtin")
                        echo builtin "$arg"
                        ;;
                "file")
                        builtin type -path "$arg"
                        ;;
                *)
                        # OK, we could have a variable, or we could have nada
                        if [ "$(eval echo \${$arg+set})" = "set" ] ; then
                                # It is a variable, and it is set
                                echo -n "$arg="
                                eval echo '\"'\$$arg'\"'
                        else
                                echo whatis: $arg: not found
                                fail=1
                        fi
                        ;;
                esac
        done
        return $fail
}