About Ruby regular expressions (metacharacters, captures, related methods)

Introduction

Now that I've started to learn regular expressions, I'll write about how to use them as a reminder.

Sample code

Suppose you have a profile like this:

text = <<TEXT
Birthday:Born May 6, 1234
Postal code:789-1111
TEXT

If you want to extract only numbers from your date of birth

(\d+)Year(\d+)Month(\d+)Day
#=> 1234,5,6 is extracted.
#=>Below, the kanji for the date will also match.
\d+Year\d+Month\d+Day
#=>May 6, 1234

Regular expression metacharacter meaning

** \ d ** ・ ・ ・ Half-width numbers (regardless of digits) ** + ** ・ ・ ・ The previous character or pattern is continuous at least once ** () ** ・ ・ ・ Capture or group the internally matched character strings ** Year, month, day ** ・ ・ ・ Not a metacharacter, just a character string

If you want to remove the hyphen "-" between the zip codes

p text[/\d{3}-\d{4}/].gsub('-','')
#=>7891111

Meaning of regular expression metacharacters and methods

** / (Regular expression) / ** ・ ・ ・ Create a regular expression object by enclosing it in / (called "regular expression literal in Ruby") ** [] ** ・ ・ ・ String class method that extracts the part that matches the regular expression from the character string. The alias method is the ** slice ** method. ** {3}, {4} ** ・ ・ ・ The previous character (\ d in this case) continues for the number enclosed in {}. - ・ ・ ・ Not a metacharacter, just a hyphen. (Note that hyphens may represent "character range" depending on how they are written.) ** gsub ('1st argument','2nd argument') ** ・ ・ ・ Replace the character string that matches the 1st argument with the character string of the 2nd argument. In the above case, the character string "-" is converted to "" (meaning deletion). The ** slice ** method and ** gsub ** method each have a "destructive method ()". () A method that changes the state of the called object. Add "!" At the end.

A tool for testing regular expressions

Regular expressions can be visually confirmed using tools that can be tried and errored because they make full use of metacharacters.

https://rubular.com/

At the end

A regular expression that works well when searching and replacing strings. I wanted to master it in the near future, so I first described the basic learning content. Thank you for reading this far.