Using Regular Expressions: Ensuring that a specific character is immediately followed by one or multiple digits

Question

Check out the regular expression I created:

^[0-9\(\)\*\+\/\-\sd]*$

This regex is designed to match patterns such as: '2d6', '(3d6) + 3', and more.

However, it also mistakenly matches: '3d'

My goal is to ensure that any instance of 'd' is always immediately followed by at least one digit.

Answer 1

Answer №1

If you are looking to find a specific string of characters within a limited set (e.g., (2511****d4+++(), but also require the presence of a number after the letter d, you can divide your regex into two options using (…|…):
```
^([\d\*\+\/\-\s]|d\d+)*$
  ------------------ ----
           |           |
  individual characters   dN
```
However, if your goal is to identify a more defined pattern, like number d number with optional parentheses and an optional operator followed by another number, you will need a customized regex. For example:
```
^(\d+d\d+|$ *\d+d\d+ *$)( *[\+\-\*\/] *\d+)?$
  ------- ---------------    ----------  ---
     |           |                |       |
    NdN       ( NdN )          operator   N
```
Alternatively, if your string represents a mathematical expression, you may consider using a recursive descent parser for handling nested expressions.

Answer 2

If you are looking to find a specific string of characters within a limited set (e.g., (2511****d4+++(), but also require the presence of a number after the letter d, you can divide your regex into two options using (…|…):
```
^([\d\*\+\/\-\s]|d\d+)*$
  ------------------ ----
           |           |
  individual characters   dN
```
However, if your goal is to identify a more defined pattern, like number d number with optional parentheses and an optional operator followed by another number, you will need a customized regex. For example:
```
^(\d+d\d+|$ *\d+d\d+ *$)( *[\+\-\*\/] *\d+)?$
  ------- ---------------    ----------  ---
     |           |                |       |
    NdN       ( NdN )          operator   N
```
Alternatively, if your string represents a mathematical expression, you may consider using a recursive descent parser for handling nested expressions.