Zeeshan

Posted on Feb 19, 2023 • Edited on Jul 5, 2024 • Originally published at acidop.codes

Regex Cheatsheet 101: Your Ticket to Regex Mastery

#programming #tutorial #beginners #webdev

Regex Cheatsheet 101

Are you tired of trying to make sense of regex? Don't worry, you're not alone! Regex is like a secret language that only a select few seem to understand.

We've got you covered with our Regex Cheatsheet 101!

NOTE: This blog is visually unappealing due to the formatting of dev so I am also linking my blog where it looks better.

Anchors

^: Start of string or line. Think of it as a hat for your text. It marks the beginning of a line.
\A: Start of string. A fancier hat that marks the beginning of a string.
$: End of string or line. The opposite of ^, it marks the end of a line.
\Z: End of string. The fancier cousin of $ that marks the end of a string.
\b: Word boundary. It's like a little force field around a word that tells you where it begins and ends.
\B: Not word boundary. The opposite of \b.
\<: Start of word. Similar to ^ and \A, but specifically for words.
\>: End of word. The opposite of \<.

Character Classes

\c: Control character. A character that controls your text. Watch out, it's in charge!
\s: Whitespace. Spaces, tabs, and other invisible characters that make your text look nice and neat.
\S: Not whitespace. Anything that's not a space, tab, or other invisible character.
\d: Digit. The numbers 0-9.
\D: Not digit. Anything that's not a number.
\w: Word. Letters, numbers, and underscores.
\W: Not word. Anything that's not a letter, number, or underscore.
\x: Hexadecimal digit. A fancy name for numbers and letters (A-F, a-f) that are used in hex code.
\O: Octal digit. Numbers in base 8. Fun fact: octopuses are also good with digits!

Quantifiers

*: 0 or more. Like a buffet that you can go back to as many times as you want.
+: 1 or more. Like a VIP lounge that only lets in the cool kids who have something to offer.
?: 0 or 1 (optional). Like a checkbox that you can check or leave empty.
{3}: Exactly 3. The perfect number of times to do something.
{3,}: 3 or more. Like a marathon that never seems to end.
{2,5}: 2, 3, 4 or 5. Like a multiple-choice question with several correct answers.

Special Characters

\n: New line. The line break that you use when you want to start a new paragraph.
\r: Carriage return. A fancy name for the Enter key.
\t: Tab. The button that you press when you want to indent your text.
\v: Vertical tab. A rarely used character that you probably won't need to worry about.
\f: Form feed. A character that's mostly used in old printers. Don't worry about it.

Assertions

?=: Lookahead assertion. Like a crystal ball that tells you what's coming up next in your text.
?!: Negative lookahead. The opposite of ?=. It tells you what's not coming up next in your text.
?<=: Lookbehind assertion. Like a time machine that takes you back to the beginning of a word or phrase.
?<!: Negative lookbehind. The opposite of ?<=. It tells you what's not behind you in your text.

Groups and Capture

(): Group. A way to group parts of your regex together.
(?:): Non-capturing group. Like a regular group, but it doesn't create a capture group.
\n: Backreference. A way to reference a previous capture group.
(?P<name>): Named capture group. A way to give a capture group a name.

Alternation

|: Alternation. A way to match one thing or another. It's like a fork in the road.
[]: Character set. A way to match one character out of a set of characters.
[^]: Negated character set. The opposite of []. Matches anything not in the set.

Flags

i: Case-insensitive. Matches both upper and lowercase letters.
m: Multiline. Allows ^ and $ to match the beginning and end of lines.
s: Dot-all. Allows . to match newline characters.
x: Verbose. Allows you to write your regex in multiple lines and add comments.