how to match a whole substring with delimiter in bash - grep

Question

I have a String like this
"ABCD EFGH IJKL MNOP"
I get user input to match with each of these substrings as whole and not part.
How do I do this?
This is what I am doing currently
printf "\n Enter user input:"
read userinput
INPUT=$userinput
if echo "ABCD EFGH IJKL MNOP" | grep -q "$INPUT"; then
echo "Matching...";
else
echo "Invalid entry ";
fi
The problem with the above code is it will match a partial substring like "ABC",
"GH" etc which I do not want. I just need the user input to compare with whole substrings separated by delimiter.

Answer 1

Use -w to match an entire word in grep
echo "ABCD EFGH IJKL MNOP" | grep -w "$INPUT";
Example
>>> INPUT=ABC
>>> echo "ABCD EFGH IJKL MNOP" | grep -w "$INPUT";
>>>
>>> INPUT=ABCD
>>> echo "ABCD EFGH IJKL MNOP" | grep -w "$INPUT";
ABCD EFGH IJKL MNOP

Answer 2

grep -w
-w, --word-regexp
Select only those lines containing matches that form whole
words. The test is that the matching substring must either be
at the beginning of the line, or preceded by a non-word
constituent character. Similarly, it must be either at the end
of the line or followed by a non-word constituent character.
Word-constituent characters are letters, digits, and the
underscore.
Similar link: grep -w with only space as delimiter