Polyglot CheatSheet - RegEx

• .: any character
• ^: beginning of a line or string
• $: end of a line or string
• |: or
• ?: match 0 or 1 times
• +: match at least once
• *: match 0 or multiple times
• (): group
• [...]: one of the characters
• [^...]: anything but the characters listed
• \w: alphanumeric character plus _, equivalent to [A-Za-z0-9_]
• \W: non-alphanumeric character excluding _, equivalent to [^A-Za-z0-9_]
• \s: whitespace
• \S: anything BUT whitespace
• \d: digit, equivalent to [0-9]
• \D: non-digit, equivalent to [^0-9]
• \A: Matches the beginning of a string (but not an internal line).
• \z: Matches the end of a string (but not an internal line).
• \b: word boundary

• {M,N}: minimum M matches and maximum N matches

  • {M,}: match at least M times
  • {0,N}: match at most N times

Greedy vs Lazy

• .*: match as long as possible
• .*?: match as short as possible

Basic vs Extended Regex

The only difference between basic and extended regular expressions is in the behavior of a few characters: ‘?’, ‘+’, parentheses, and braces (‘{}’).

• basic regular expressions: should be escaped to behave as special characters
• extended regular expressions: should be escaped to match a literal character.

• sed

  • sed: basic
  • sed -r: extended

• grep

  • grep: basic
  • egrep or grep -E

Regular expressions: PCRE vs. ERE/BRE # Conciseness matters:

\d === [0-9]
\w === word-constituent
\W === non-word-constituent
\b === zero-width word-boundary (like \< and \>)
\s === whitespace
\S === non-whitespace

Get to know regular expressions well (esp. EREs and PCREs) Which of these do you prefer? - /'.?'/ - /'^''/ (e.g., write a C-comment-remover: easy with PCRE's .*? )

Javascript

Literal vs. Constructor

• Literal: re = /.../g

• Constructor: re = new RegExp("...")

  • can use string concat: re = new RegExp("..." + some_variable + "...")

Local vs. Global

• re = /.../: re.match(str) will return a list of captures of the FIRST match
• re = /.../g: re.match(str) will return a list of matches but NOT captures

match vs. exec

• match: as stated above
• exec: return captures, exec multiple times

Example

var match;
while ((match = re.exec(str)) !== null) {}

Javascript

• str.search
• str.match
• str.replace

Example: split country name and country code in strings like "China (CN)"

> s = "China (CN)";
'China (CN)'
> match = s.match(/\((.*?)\)/)
[ '(CN)', 'CN', index: 6, input: 'China (CN)', groups: undefined ]
> match[1]
'CN'
> s.substring(0, match.index).trim()
'China'