请教如何判断读入的一个字符串（如人名）合法？‘合法’定义为：此字符串只包含有字母或空格。此字符串的长度不定.

s="123 456 abc efg"

len=`echo $s | awk '{print length( $0 )}'`

start=1

while [ $start -le $len ]
do
        char=`echo $s | cut -c$start-$start`

        echo $char

                case $char in
                [0-9])
                        echo digital;;
                [a-z])
                        echo letter;;
                ' ')
                        echo space;;
                *)      
                        echo error;;
                esac

        start=`expr $start + 1`
done

read name
test "$name" == "$(echo $name  | egrep '[[:alpha:] ]+' -o)"