(A) To split a sentence into its words (space separated) you can simply use the default IFS by using
array=( $string )
Example running the following snippet
#!/bin/bash
sentence="this is the \"sentence\" 'you' want to split"
words=( $sentence )
len="${#words[@]}"
echo "words counted: $len"
printf "%s\n" "${words[@]}" ## print array
will output
words counted: 8
this
is
the
"sentence"
'you'
want
to
split
As you can see you can use single or double quotes too without any problem
Notes:
-- this is basically the same of mob's answer, but in this way you store the array for any further needing. If you only need a single loop, you can use his answer, which is one line shorter :)
-- please refer to this question for alternate methods to split a string based on delimiter.
(B) To check for a character in a string you can also use a regular expression match.
Example to check for the presence of a space character you can use:
regex='\s{1,}'
if [[ "$sentence" =~ $regex ]]
then
echo "Space here!";
fi