Way for regex with read-CodePudding

I am trying to catch only names starting from"d" with a length 3 to 5 letters in one line:

Currently, I have this line in my script which works for each provided user name:

read -p "Enter user: " user

For example, is it possible to use a regex after the user? Example:

read -p "Enter user: " user | grep $user =~ "(d\w{3,5})"

I have read this post but does not tell me if it is possible.

CodePudding user response：

After the value of user is set, you can examine its value.

 read -p "Enter user: " user
 if [[ $user =~ ^.{3,5}$ ]]; then
   echo "user between 3 and 5 characters"
 fi

The regular expression is not implicitly anchored to either end of the string, so you need to use ^ and $ to check that the entire string is 3-5 characters, not just that the string as a substring of 3-5 characters.

In this case, you don't even need a regular expression.

if (( 3 <= ${#user} && ${#user} <=5 )); then
    ...
fi

CodePudding user response：

I changed the regex to ^d[a-zA-Z]{2,4}$ which consists of:

^d - line must START with a lowercase "d"
[a-zA-Z]{2,4} - there must be 2-4 letters after the "d" and can be in either lowercase or uppercase, numbers or symbols not permitted
$ - reject any trailing characters

read -p "Enter user: " user
while ! [[ $user =~ ^d[a-zA-Z]{2,4}$ ]]; do
    echo "Only names starting with "d" with a total length of 3 to 5 letters"
    read -p "Enter user: " user
done