Week 6 Cheatsheet

There are more examples and details in the presentations, this is just a short and quick reminder

Anchors🔗

• ^ - Start of string
• $ - End of string
• \b - Word boundary
• \B - Not word boundary

Assertions🔗

• ?= - Lookahead assertion
• ?! - Negative lookahead
• ?<= - Lookbehind assertion
• ?!= - Negative lookbehind

Examples

• ucu(?=rules) matches ucurules
• ucu(?=rules) doesn’t match ucu
• (?<=linux)club matches linuxclub
• (?<=linux)club doesn’t match roboclub

Groups and Ranges🔗

• . - Any character except newline
• (a|b) - a or b
• (...) - Group
• [abc] - a or b or c
• [^abc] - Not (a or b or c)
• [a-q] - a or b or ... up to q
• [A-Q] - The same, but for uppercase letters
• [2-7] - The same, but for digits
• \x - Allows to reuse group number x

Examples

• [A-D] matches A, B, C or D
• (abc)\1 matches abcabc

Character classes🔗

• \s - White space
• \d - Digit
• \w - Word
• \S \D \W - Not whitespace, digit or word respectively

Quantifiers🔗

• * - 0 or more
• + - 1 or more
• ? - 0 or 1
• {3} - Exactly 3
• {3,} - 3 or more
• {3,5} - 3,4 or 5

Escape sequences and common metacharacters🔗

• \ - Escape the following metacharacter
• {}[]()^$.*+?|\ - Common metacharacters to escape to use their literal meaning

String replacement🔗

• $n - nth group
• $1 - will capture first group - abc in (abc)(xyz)

Examples:

• If we have a string ucu doesnt rule and replace the match (ucu) doesnt (rule) with the $1 $2s pattern, the result will be: ucu rules