README.md

grep -P to allow PCRE

Regular expressions are a series of characters that define patterns to search for in text.

1. Basic Usage
   1. Single characters
      1. A
      2. 1
      3. \t
   2. Multiple characters
      1. [abc]
      2. [157]
   3. Ranges
      1. [a-z]
      2. [A-Z]
      3. [a-zA-Z]
   4. Any character except line terminators
      1. .
   5. NOT
      1. How would I match consonants?
         1. [b-df-hj-np-tv-z] vs [^aeiou]
      2. [^2-8]
   6. Escaping characters
      1. \.
      2. \[
2. Meta-sequences
   1. \s and \S whitespace
   2. \d and \D digits
   3. \w and \W word characters [a-zA-Z1-9_]

• Phone number checker WITHOUT quantifiers

  • Form to match: 123-456-7890

  • Answer!

    \d\d\d-\d\d\d-\d\d\d\d

3. Quantifiers (remember they need to go outside the brackets)
   1. ? Zero or one
   2. * Zero or more
   3. + One or more
   4. {3} Exactly 3
   5. {3,} 3 or more
   6. {,3} At most 3, zero included
   7. {3,6} Between 3-6 times, inclusive

• Phone number checker WITH quantifiers

  • Form to match: 123-456-7890

  • Answer!

    \d{3}-\d{3}-\d{4}

  • Form to match: Same but with optional US country code at beginning 1123-456-7890

  • Answer!

    1?\d{3}-\d{3}-\d{4}

4. Anchors
   1. ^ Beginning of line
   2. $ End of line
5. Groups
   1. So far you could only quantify single characters at a time. You can quantify whole groups.
      1. [123]+ vs (123)+