Can regex matching characters be made easier to understand?

Question

Can regex matching characters be made easier to understand?

I am working on creating an ECMAScript (JavaScript) flavored regex to evaluate the complexity of my password based on specific criteria:

    Characters Used          Password Strength Length
   ABC  abc  123  #$&      WEAK  ...
1   x                      1-5   ...   
2        x                 1-5
3             x            1-7
4                  x       1-5
5   x    x                 1-4   
6   x         x            1-4
7   x              x       1-4
8        x    x            1-4 
9        x         x       1-4       
10            x    x       1-4     
11  x    x    x            1-4           
12  x    x         x       1-3   
13  x        x     x       1-4           
14      x    x     x       1-4  
15  x   x    x     x       1-3

Therefore, passwords like 2, ABCD, 0123456, abCd, aA#, etc. should be considered weak. Passwords that are longer while meeting the specified criteria e.g., 012345678, aA1#, should not.

My current intricate regex pattern (organized by groups according to the above table) looks something like this:

/^(([A-Za-z&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]{1,3})|([a-z0-9&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]{1,4})|([A-Z0-9&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]{1,4})|([a-zA-Z0-9]{1,4})|([a-z]{1,5})|([A-Z]{1,5})|([0-9]{1,7})|([&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]{1,5}))$/

Matches rows in the above table: 12

/([A-Za-z&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]{1,3})/

Matching rows: 14, 9

/([a-z0-9&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]{1,4})/

Matching rows: 13, 10, 7

/([A-Z0-9&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]{1,4})/

Matching rows: 11, 8, 6, 5

/([a-zA-Z0-9]{1,4})/

Matching rows: 2

/([a-z]{1,5})/

Matching rows: 1

/([A-Z]{1,5})/

Matching rows: 3

/([0-9]{1,7})/

Matching rows: 4

/([&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]{1,5})/

Is there a way to reuse the special characters I defined inside []

[&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]

, so that I don't have to list them out within each individual group?

javascript regex

Answer 1

Answer №1

Is there a way to reuse specified special characters inside [] without rewriting them in every group?

No, you cannot do this with a regular expression literal.

However, you can achieve this using the RegExp constructor. To avoid escaping backslashes, you can utilize String.raw like so:

const chars = String.raw`[the chars]`;
const rex = new RegExp(String.raw`^...${chars}...${chars}...$`);

You can even create a custom tag function for this purpose, as demonstrated below (excerpt from Chapter 10 of my latest book; refer to my profile for more information):

const createRegex = (template, ...values) => {
    const source = String.raw(template, ...values);
    const match = /^\/(.+)\/([a-z]*)$/.exec(source);
    if (!match) {
        throw new Error("Invalid regular expression");
    }
    
    const [, expr, flags = ""] = match;
    return new RegExp(expr, flags);
};

With this custom function, you can simplify regex creation like this:

const chars = String.raw`[the chars]`;
const rex = createRegex`/^...${chars}...${chars}...$/`;

Answer 2

Is there a way to reuse specified special characters inside [] without rewriting them in every group?

No, you cannot do this with a regular expression literal.

However, you can achieve this using the RegExp constructor. To avoid escaping backslashes, you can utilize String.raw like so:

const chars = String.raw`[the chars]`;
const rex = new RegExp(String.raw`^...${chars}...${chars}...$`);

You can even create a custom tag function for this purpose, as demonstrated below (excerpt from Chapter 10 of my latest book; refer to my profile for more information):

const createRegex = (template, ...values) => {
    const source = String.raw(template, ...values);
    const match = /^\/(.+)\/([a-z]*)$/.exec(source);
    if (!match) {
        throw new Error("Invalid regular expression");
    }
    
    const [, expr, flags = ""] = match;
    return new RegExp(expr, flags);
};

With this custom function, you can simplify regex creation like this:

const chars = String.raw`[the chars]`;
const rex = createRegex`/^...${chars}...${chars}...$/`;

Answer 3

Answer №2

If you are utilizing a regex engine like Perl or Ruby, leveraging subroutines can help you achieve the desired results to a considerable extent. Subroutines essentially entail repeating patterns within a regex.

You might be familiar with backreferences, but it's important to note that subroutines differ from backreferences. With backreferences, the matched content of a captured group is used, whereas with subroutines, the pattern matching is reiterated.

Let's consider an example:

Sample string: abcd-defg
Regex in Ruby:
```
/(?<dd>[a-z]+)-\g<dd>/
```
. This will result in a successful match.
The \g<dd> section represents the subroutine call in Ruby for the group named dd. (The syntax may vary depending on the regex engine you are using.)

For more information, you can refer to the following resources:

In your specific scenario, naming each group when it initially appears in the regex and then referencing it as a subroutine subsequently could be beneficial. For instance:

[A-Z] could be denoted as A
[a-z] could be represented as a
[0-9] could be termed as n
and the special character set as s (assuming correct pattern identification)

Therefore, the pattern for 12

/([A-Za-z&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]{1,3})/

could transform into

/((\g<A>|\g<a>|\g<s>)){1,3})/

Meaning, A OR a OR s repeated 1-3 times.

And the pattern for 11, 8, 6, 5 /([a-zA-Z0-9]{1,4})/ would evolve into

/((\g<a>|\g<A>|\g<n>)){1,4})/

Signifying, a OR A OR n repeated 1-4 times.

Answer 4

If you are utilizing a regex engine like Perl or Ruby, leveraging subroutines can help you achieve the desired results to a considerable extent. Subroutines essentially entail repeating patterns within a regex.

You might be familiar with backreferences, but it's important to note that subroutines differ from backreferences. With backreferences, the matched content of a captured group is used, whereas with subroutines, the pattern matching is reiterated.

Let's consider an example:

Sample string: abcd-defg
Regex in Ruby:
```
/(?<dd>[a-z]+)-\g<dd>/
```
. This will result in a successful match.
The \g<dd> section represents the subroutine call in Ruby for the group named dd. (The syntax may vary depending on the regex engine you are using.)

For more information, you can refer to the following resources:

In your specific scenario, naming each group when it initially appears in the regex and then referencing it as a subroutine subsequently could be beneficial. For instance:

[A-Z] could be denoted as A
[a-z] could be represented as a
[0-9] could be termed as n
and the special character set as s (assuming correct pattern identification)

Therefore, the pattern for 12

/([A-Za-z&*@\^}\]\\):,$=!><–{[(%+#;\/~_?.]{1,3})/

could transform into

/((\g<A>|\g<a>|\g<s>)){1,3})/

Meaning, A OR a OR s repeated 1-3 times.

And the pattern for 11, 8, 6, 5 /([a-zA-Z0-9]{1,4})/ would evolve into

/((\g<a>|\g<A>|\g<n>)){1,4})/

Signifying, a OR A OR n repeated 1-4 times.

Can regex matching characters be made easier to understand?

Answer №1

Answer №2

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