More RegEx #
There are certainly more practical aspects of RegEx. Here, we discuss additional syntax elements and provide examples of how to use them effectively in various scenarios.Capturing Groups #
A capturing group is a portion of a RegEx pattern enclosed in parentheses (...). Capturing groups serve two main purposes:
- They allow you to apply quantifiers and alternation to a group of characters or subpatterns.
- They capture the matched text within the group for later use, such as for extracting, replacing, or referencing the matched content.
Extracting Dates and Their Components #
Suppose you have dates formatted as MM-DD-YYYY and want to extract the entire date and its components (month, day, and year). The following RegEx pattern uses capturing groups to achieve this:
(\d{2})-(\d{2})-(\d{4})
-
(\d{2}): Capturing group that matches two digits (the month, the date)… -
-: Matches a hyphen (the separator).
Reformatting Dates #
Suppose you have dates formatted as
MM-DD-YYYYand want to reformat them to theYYYY-MM-DDformat. This pattern is the same as in the previous example.
In a programming language that supports RegEx, such as Python or JavaScript, you can use the captured groups to reformat the date:
import re
date_string = "12-25-2021"
pattern = r"(\d{2})-(\d{2})-(\d{4})"
reformatted_date = re.sub(pattern, r"\3-\1-\2", date_string)
print(reformatted_date) # Output: "2021-12-25"
Non-capturing Groups #
(?:...) creates a non-capturing group, which means the matched content within the group won’t be captured for later use. Non-capturing groups are useful when you need to apply quantifiers or alternation to a group of characters but don’t need to reference the matched content.
Example: The RegEx pattern “^(?:+1\s)?\d{3}-\d{3}-\d{4}$” matches both US phone numbers with and without the “+1” country code prefix but doesn’t capture the prefix.
Matching dates with different separators #
Suppose you have dates formatted as
MM-DD-YYYYorMM/DD/YYYY, and you want to match the dates without capturing the separators.
(?:\d{2})(?:-|\/)(?:\d{2})(?:-|\/)(?:\d{4})