if regex bash code example

Example 1: using regex in bash conditional statement

pat="[0-9a-zA-Z ]"
if [[ $x =~ $pat ]]; then ...

Example 2: bash regex if condition

Use following structure:
if [[ $digit =~ [0-9] ]]; then //run if a digit included in $digit string
    echo "$digit is a digit"
else
    echo "oops"
fi