Regular Expressions (regex) - robbiehume/CS-Notes GitHub Wiki

Links

• https://regexone.com/
• https://regex101.com/
• https://www.regular-expressions.info/tutorial.html

Notes

• .: any character
• \.: period character
• [abc]: only a, b, and c
• [^abc]: any character but a, b, and c
• \d: any digit
• \D: any non-digit character
• [a-z]: characters a to z; can be any range (a-c)
• [0-9]: numbers 0 to 9; can be any range (1-3)
• \w: any alphanumeric character
• \W: any non-alphanumeric character
• {m}: m repetitions; a{3} will match the character exactly 3 times
  • Ex. [abc]{5}: 5 characters, each of which can be an a, b, or c
• {m,n}: m to n repetitions; a{1,3} will match the character no more than 3 times, but no less than once
  • Ex. .{2,6}: between 2 and 6 of any character
• *: 0 or more repetitions;
  • Ex. .*: 0 or more of any character
• +: 1 or more repetitions
  • Ex. [abc]+: 1 or more of any a, b, or c characters
• ?: optional character
  • Ex. ab?c will match either "abc" or "ac" because the b is considered optional
• \s: any whitespace character (space, tab, newline, etc.)
  • Ex. .*: any amount of whitespace
• \S: any non-whitespace character
• \b: word boundary character; helps find words starting or ending with certain characters
  • For vim search, it uses \< and \> instead
  • Ex: \b[Aa]uth finds any word starting with "Auth" or "auth"
• ^: starts with; is different than the ^ in [^abc]
  • Ex. ^Hello: only lines that start "Hello"
• $: ends with
  • Ex. Bye\.$: only lines that end with "Bye."
• Can combine ^ and $: ^mission: successful$
• (): () can be used for match groups to extract info from a string
  • Ex: ^(IMG\d+\.png$ will only capture the image name
• Nested groups: exgtract multiple layers of info
  • Ex: (\w+ (\d+)) turns Jan 1999 into 2 groups: Jan 1999 and 1999
• |: can use a pipe to specify multiple different options
  • Ex: (cats|dogs)$ matches "I love cats" and "I love dogs"
• (?i): case-insensitive mode; add it to beginning of regex