Escaping Special Characters — When and How · RegEx Quest

Backslash makes special literal, and vice versa

Two facts:

To match a metacharacter literally, put a backslash in front: \. matches a dot, \$ matches a dollar sign, \\ matches a backslash.
To create a special meaning out of an ordinary letter, put a backslash in front: \d means digit, \b means word boundary, \n means newline.

The backslash is the universal mode flip.

Raw strings save your sanity

In Python, JavaScript template literals, and most languages, the backslash is ALSO the string-escape character. So "\d" in a Python string is interpreted by the string parser before regex sees it — sometimes harmlessly, sometimes catastrophically.

Always use raw strings (or the equivalent) for regex patterns. Python: r"\d+". Rust: r"\d+". JavaScript regex literals: /\d+/ (the slashes provide the same protection).

Without raw strings: "\d" in Python is the same as "\\d" by accident, but "\b" is the ASCII backspace character (8) — your pattern is silently wrong.

Programmatic escaping

If you're building a regex from user input or a variable, use the engine's escape function: Python re.escape(), modern JavaScript RegExp.escape(), or Go regexp.QuoteMeta(). Older JavaScript runtimes need a vetted polyfill. Never concatenate raw user input into a pattern.

Code

Escaping done right·python

import re

# Match a literal $19.99
re.findall(r'\$\d+\.\d{2}', 'price was $19.99 today')
# ['$19.99']

# WITHOUT raw string — silently wrong
import re
pattern = "\d+"  # Python sees: "\d+" → backslash interpreted by str
print(repr(pattern))  # '\\d+' actually  (depends on version)

# Programmatic escaping for user input
user_input = 'price: $19.99'
safe = re.escape(user_input)
print(safe)
# 'price:\\ \\$19\\.99'
re.findall(safe, 'note: price: $19.99 today')

Escaping Special Characters — When and How

Backslash makes special literal, and vice versa

Raw strings save your sanity

Programmatic escaping

Code

External links

Exercise

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