REGEX FOR BEGINNERS

# REGEX FOR BEGINNERS ##### And bullies --- ### Why use regex * speed up text manipulation * find stuff quickly * replace stuff quickly * make everyone jealous ---- `/^(?=.*(\[Rep SG:[^\]]*\]))(?=.*(\[Rep CR:[^\]]*\]))(?=.*(\[Rep TY:[^\]]*\])).*$/` --- ### Standard text search X => X --- blastimir blast you bleeding blastimir! ---- blastimir blast you bleeding blastimir! ---- blastimir blast you bleeding blastimir! ---- blastimir blast you bleeding blastimir! ---- blastimir blast you bleeding blastimir! ---- blastimir blast you bleeding blastimir! ---- blastimir blast you bleeding blastimir! ---- blastimir blast you bleeding blastimir! ---- blastimir blast you bleeding blastimir! ---- blastimir blast you bleeding blastimir! ---- ... ---- blastimir blast you bleeding blastimir! --- ### Problem blast blast you bleeding blastimir! ---- ### ~~Standard text search~~ --- ### Regex Syntax X =/= X `[ ] \ ^ $ . | ? * + ( ) { }` ---- ```plaintext [...] => one of \d => number A-Z => any uppercase char a-z => any lowercase char \t => tab \n => line feed ... ``` --- ### Simple example Looking for: > drink drank drunk Not interested in: > drinking drunkard antidrink --- ### Standard search * multiple searches (drink, drank, drunk) * false positives --- ### Regex * one search to rule them all ↓ ----  ```diff drink drank drunk drek drinking drunkard antidrink ``` ####   ----  ```diff +drink drank drunk drek +drinking drunkard +antidrink ``` #### `drink` ----  ```diff +drink +drank drunk drek +drinking drunkard +antidrink ``` #### `dr[ia]nk` ----  ```diff +drink +drank +drunk drek +drinking +drunkard +antidrink ``` #### `dr[iau]nk` ----  ```diff +drink +drank +drunk drek drinking drunkard +antidrink ``` #### `dr[iau]nk\b` ----  ```diff +drink +drank +drunk drek drinking drunkard antidrink ``` #### `\bdr[iau]nk\b` --- ### Example 2 Filter files ----  ```diff german.jpg midget.png bondage.jpeg definitelyajpg.rar nudes.jpg.zip rtfm.txt send_nudes.eml goaway.tar.gz ``` ####   ----  ```diff +german.jpg midget.png bondage.jpeg +definitelyajpg.rar +nudes.jpg.zip rtfm.txt send_nudes.eml goaway.tar.gz ``` #### `jpg` ----  ```diff +german.jpg midget.png bondage.jpeg definitelyajpg.rar +nudes.jpg.zip rtfm.txt send_nudes.eml goaway.tar.gz ``` #### `\.jpg` ----  ```diff +german.jpg midget.png bondage.jpeg definitelyajpg.rar nudes.jpg.zip rtfm.txt send_nudes.eml goaway.tar.gz ``` #### `\.jpg$` ----  ```diff +german.jpg midget.png +bondage.jpeg definitelyajpg.rar nudes.jpg.zip rtfm.txt send_nudes.eml goaway.tar.gz ``` #### `\.jpe?g$` ----  ```diff +german.jpg +midget.png +bondage.jpeg definitelyajpg.rar nudes.jpg.zip rtfm.txt send_nudes.eml goaway.tar.gz ``` #### `\.(jpe?g)|(png)$` --- ### Example 3 Looking for drunk campaigns ----  ```diff Campaign: drink Campaign: drink too much Campaign: #69 Campaign: #666 Not a Campaign: oops Your mom is a Campaign Campaign: 666 Campaign: ``` ####   ----  ```diff +Campaign: drink +Campaign: drink too much +Campaign: #69 +Campaign: #666 +Not a Campaign: oops +Your mom is a Campaign +Campaign: 666 +Campaign: ``` #### `Campaign` ----  ```diff +Campaign: drink +Campaign: drink too much +Campaign: #69 +Campaign: #666 +Not a Campaign: oops Your mom is a Campaign +Campaign: 666 +Campaign: ``` #### `Campaign:` ----  ```diff +Campaign: drink +Campaign: drink too much +Campaign: #69 +Campaign: #666 Not a Campaign: oops Your mom is a Campaign +Campaign: 666 +Campaign: ``` #### `^Campaign:` ----  ```diff Campaign: drink Campaign: drink too much Campaign: #69 Campaign: #666 Not a Campaign: oops Your mom is a Campaign Campaign: 666 +Campaign: ``` #### `^Campaign:$` ----  ```diff +Campaign: drink +Campaign: drink too much Campaign: #69 Campaign: #666 Not a Campaign: oops Your mom is a Campaign +Campaign: 666 Campaign: ``` #### `^Campaign: \w+` ----  ```diff +Campaign: drink Campaign: drink too much Campaign: #69 Campaign: #666 Not a Campaign: oops Your mom is a Campaign +Campaign: 666 Campaign: ``` #### `^Campaign: \w+$` ----  ```diff +Campaign: drink +Campaign: drink too much Campaign: #69 Campaign: #666 Not a Campaign: oops Your mom is a Campaign +Campaign: 666 Campaign: ``` #### `^Campaign:( \w+){1}` ----  ```diff +Campaign: drink Campaign: drink too much Campaign: #69 Campaign: #666 Not a Campaign: oops Your mom is a Campaign +Campaign: 666 Campaign: ``` #### `^Campaign:( \w+){1}$` ----  ```diff Campaign: drink +Campaign: drink too much Campaign: #69 Campaign: #666 Not a Campaign: oops Your mom is a Campaign Campaign: 666 Campaign: ``` #### `^Campaign:( \w+){3}` ----  ```diff +Campaign: drink +Campaign: drink too much Campaign: #69 Campaign: #666 Not a Campaign: oops Your mom is a Campaign +Campaign: 666 Campaign: ``` #### `^Campaign:( \w+)+` ----  ```diff +Campaign: drink +Campaign: drink too much +Campaign: #69 +Campaign: #666 Not a Campaign: oops Your mom is a Campaign +Campaign: 666 +Campaign: ``` #### `^Campaign:( \w+)*` ----  ```diff Campaign: drink Campaign: drink too much Campaign: #69 Campaign: #666 Not a Campaign: oops Your mom is a Campaign +Campaign: 666 Campaign: ``` #### `^Campaign: \d+` ----  ```diff Campaign: drink Campaign: drink too much +Campaign: #69 +Campaign: #666 Not a Campaign: oops Your mom is a Campaign +Campaign: 666 Campaign: ``` #### `^Campaign: .\d+` ----  ```diff Campaign: drink Campaign: drink too much +Campaign: #69 +Campaign: #666 Not a Campaign: oops Your mom is a Campaign Campaign: 666 Campaign: ``` #### `^Campaign: #\d+` ----  ```diff Campaign: drink Campaign: drink too much +Campaign: #69 +Campaign: #666 Not a Campaign: oops Your mom is a Campaign +Campaign: 666 Campaign: ``` #### `^Campaign: #?\d+` --- ### Example 4 Duplicate words ----  ```diff That is not a test. +That is not not a test. +This is a test. +This is is a test. ``` #### `(\w+)\s\1` ----  ```diff That is not a test. +That is not not a test. This is a test. +This is is a test. ``` #### `(\b\w+\b)\s\1` --- ### Scary Example 5 Password validation ----  ##### `^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$` ----  ```plaintext ^ <- start of string (?=.*[A-Za-z]) (?=.*\d) [A-Za-z\d] {8,} $ ``` ----  ```plaintext ^ (?=.*[A-Za-z]) <- positive lookahead: find a character (?=.*\d) [A-Za-z\d] {8,} $ ``` ----  ```plaintext ^ (?=.*[A-Za-z]) (?=.*\d) <- positive lookahead: find a digit [A-Za-z\d] {8,} $ ``` ----  ```plaintext ^ (?=.*[A-Za-z]) (?=.*\d) [A-Za-z\d] <- find a character or a digit {8,} $ ``` ----  ```plaintext ^ (?=.*[A-Za-z]) (?=.*\d) [A-Za-z\d] {8,} <- repeat previous expression $ *at least* 8 times ``` ----  ```plaintext ^ (?=.*[A-Za-z]) (?=.*\d) [A-Za-z\d] {8,} $ <- end of string ``` --- ### Finite State Machines * Every regular expression is a finite state machine! ----  ```plaintext \.(jpe?g)|(png) ``` ![state-machine-images](https://github.com/dsimidzija/presentations/raw/master/assets/images/state-machine-images.png) ----  ```plaintext ^(a|b)c*d+$ ``` ![state-machine2](https://github.com/dsimidzija/presentations/raw/master/assets/images/state-machine2.png) ----  ### FSM graph for: ```plaintext \bdr[iau]nk\b ``` # ? --- ### Further points * Many more options than presented * Start simple * Use https://regex101.com/ --- ### T.Hanks ![T.Hanks](https://i.imgur.com/xn9uaPX.jpg)