Bash: How to tokenize a string variable?

[*]

$ string="john is 17 years old"
$ tokens=( $string )
$ echo ${tokens[*]}

For other delimiters, like ‘;’

$ string="john;is;17;years;old"
$ OLDIFS="$IFS"
$ IFS=';' tokens=( $string )
$ echo ${tokens[*]}
$ IFS="$OLDIFS" # restore IFS