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Regex

Regex are in simple terms "a sequence of characters that define a search pattern"

  • basic is *.gif where * means anything.
  • Position of search
    • ^ - starts with - ^Simple - any line that start with this
    • $ - ends with - park$ - any line that end with this
  • Frequency of occurrence
    • * - 0 or more - ab* a followed by zero or more b's
    • + - 1 or more - ab+ - the letter a followed by one or more b's
    • ? - 0 or 1 - ab? - zero or just one b
    • {n} - n exactly - ab{2} - the letter a followed by exactly two b's
    • {n,} - n or more - ab{2,} - the letter a followed by at least two b's
    • {n,y} - n to y occurrence - ab{1,3} - the letter a followed by between one and three b's
  • Class of characters - list or range, and are case-sensitive
    • Range - [a-z] or [A-Z] or [0-9]
    • List - [a,d,p,w] or [adpwKRM] - match any single character
    • Mix - [A-Z2-4pw] - matches range A-Z, 2-4 and literally p, and literally w
    • Except - [^abXyP-Q] and character except what is in
  • Flags to search for special types of characters without needing to list them in a range
    • . m any character
    • \s - whitespace - \S opposite
    • \w - word - \W not a word
    • \d - digit (number) - \D not a digit
    • \b - word boundary - ate\b finds ate at end of word, eg, plate but not gates.- \B not boundary
  • Other
    • \n \r \t \0 - new line, carriage, tab, null
    • | - or - The (?:cat|dog) jumps matches cat or dog
  • Regex Groups
    • In Find: you can use regex with "capturing groups," e.g. I want to find (group1) and (group2), using parentheses
    • In Replace: you can refer to the capturing groups via $1, $2 etc.
    • Eg, VS Code - to use what you found in replace use $1, eg, find <h1>(.+)</h1>, replace <b>$1</b>. Replaces <h1>Todo</h1> with <b>Todo</b>
    • more here.

Regex in JavaScript

// find and replace with space globally for all occurance
someString.replaceAll(new RegExp('[:,/,.]','g'),' ')

// replace an occurance in string
someString.replace(/h1/,'h2')

Regex in Python

import re

text = 'aaa@xxx.com bbb@yyy.net ccc@zzz.org'

# print(re.sub('pattern', 'replacement', text))
print(re.sub('[a-z]+@', 'ABC@', s))

# ABC@xxx.com ABC@yyy.net ABC@zzz.org

Snippets

  • multiline with one line \s\n+ \n
  • remove end whitespace \s+\n \n

  • Remove single line comments // from code:

    • \/\/.*$\n - Finds all single line comments starting with //.
      • \/\/ - string has //
      • .* - then has anything after that
      • $\n - then matches next line as well.

Remove Trailing whitespace

  • Find: \s+$
  • Replace: ``

Remove trailing whitespace from only those lines that have text

  • Find: (\S+)(\s+)$
  • Replace: $1
  • It finds trailing text as first group (\S+), then trailing whitespace just after text as second group (\s+) and at end of line $.
  • Then replaces both groups by just the first group $1.

Whatsapp Text from Markdown

  • This snippet lets you convert markdown to be formatted in most correct way for whatsapp chat.
  • Find ** Replace *. Finds bold, makes them bold for Whatsapp.
  • Find #+ (.+)\n Replace *$1*\n. Finds headings, replaces them with bold line.
2025-01-12 January 12, 2025