# Strings, Regular Expressions and Encodings — Ruby

Source: https://www.geekswithgeeks.com/en/ruby/p-strings

> Manipulate strings, use regular expressions and handle encodings.

## Text processing

Ruby strings have a large method set: `strip`, `squeeze`, `downcase`/`upcase`/`capitalize`, `start_with?`/`end_with?`/`include?`, `split`, `gsub`/`sub` for replacement, `tr` for character translation, `center`/`ljust`/`rjust` for alignment, `format` (or `%`) for formatting, and **heredocs** (`<<~TEXT`) for multi-line strings with indentation stripped. **Regular expressions** are first-class: `/\A\d{6}\z/` literals, `=~` and `match?` for testing (`match?` is fastest when you do not need captures), `match` with **named captures** (`(?<pin>\d{6})`), `scan` to find all matches and `gsub` with a block for computed replacements. Use **`\A` and `\z`** to anchor to the whole string; `^` and `$` match at line boundaries, a classic source of validation bugs. Strings carry an **encoding**, usually UTF-8; `length` counts characters, `bytesize` counts bytes, and `force_encoding`/`encode` handle data from other encodings. With `# frozen_string_literal: true`, build strings with interpolation or `+` rather than mutating literals.

## Validation and extraction with regexes

Whole-string anchors, named captures and scan.

```ruby
PIN = /\A\d{6}\z/
puts "411001".match?(PIN)                  # true
puts "411001\nhack".match?(/^\d{6}$/)      # true: ^ and $ match per line (unsafe for validation)
puts "411001\nhack".match?(PIN)            # false: \A and \z anchor the whole string

address = "12 MG Road, Pune 411001, Maharashtra"
if (m = address.match(/(?<city>[A-Z][a-z]+) (?<pin>\d{6})/))
  puts "#{m[:city]} - #{m[:pin]}"           # Pune - 411001
end

puts "Order o-12 and o-345 shipped".scan(/o-\d+/).inspect   # ["o-12", "o-345"]

masked = "Card 4242424242424242".gsub(/\d(?=\d{4})/, "*")  # mask all but the last 4 digits
puts masked

letter = <<~TEXT
  Dear #{"Asha"},
    Your order has shipped.
TEXT
puts letter

puts "नमस्ते".length, "नमस्ते".bytesize      # characters versus bytes
```

## Use \A and \z for validation

Validating input with `^...$` lets strings with embedded newlines pass, a known source of injection bugs (and Rails warns about it in model validations). Anchor with `\A` and `\z`.

**Quiz:** Which anchors match the start and end of the entire string in a Ruby regex?

- [ ] ^ and $
- [x] \A and \z
- [ ] < and >
- [ ] \b and \B

*Answer:* \A and \z. ^ and $ match at line boundaries; \A and \z anchor the whole string.