I defined a regular expression to check if the string only contains alphabetic characters and with length 5:

use regex::Regex;

fn main() {
  let re = Regex::new("[a-zA-Z]{5}").unwrap();
  println!("{}", re.is_match("this-shouldn't-return-true@"));
}

The text I use contains many illegal characters and is longer than 5 characters, so why does this return true?

CodePudding user response：

You have to put it inside ^...$ to match the whole string and not just parts:

use regex::Regex;

fn main() {
    let re = Regex::new("^[a-zA-Z]{5}$").unwrap();
    println!("{}", re.is_match("this-shouldn't-return-true@"));
}

Playground.

As explained in the docs:

Notice the use of the ^ and $ anchors. In this crate, every expression is executed with an implicit .*? at the beginning and end, which allows it to match anywhere in the text. Anchors can be used to ensure that the full text matches an expression.

CodePudding user response：

Your pattern returns true because it matches any consecutive 5 alpha chars, in your case it matches both 'shouldn't' and 'return'.

Change your regex to: ^[a-zA-Z]{5}$

^            start of string
[a-zA-Z]{5}  matches 5 alpha chars
$            end of string

This will match a string only if the string has a length of 5 chars and all of the chars from start to end fall in range a-z and A-Z.