/regex

Primary LanguageJavaScript

Dev

run: http-server -p 2380
view at: http://localhost:2380/demo/

Regex Syllabus

Introduction to Regex

AKA: learning the concept & reasons

  • What is it for?
    • Finding desired patterns within strings of text
    • Treats everything as sequence of characters
  • Basic syntax
    • Delimiter / ... /
    • flags / ... /igm
      • g: iterative search
      • i: ignore case (case insensitive)
      • m: multiline support

Regex Lessons

AKA: learning the commands

  • Literal identifier
    • /literal/matches "literal"
    • Matching everything .
      • /.*/
    • Searching with Or |
      • /everything|something/
    • Anchors
      • Match start of string: /^pattern/
      • Match end of string: /pattern$/
  • Carrot functions & importance of placement
    • /^literal/ will match "literal lesson"
    • /^literal/ will not match "Something literal"
    • /^[literal]/ will match anything except "literal"
    • /literal$/ will match "Something literal"
  • Escaping characters
    • Preceed character wth\ e.g.: \.
    • Matching everything
    • /./ matches all characters including whitespaces
    • escape . to match lteral period
  • Quantifiers: repeating with +
    • + matches one or more of preceeding pattern
    • l{1,3} matches one to three repeated instances of letter l
    • ? is used to make a pattern optional
      • /pie?/ matches pi
  • Shortcut classes vs long the way
    • \d vs [0-9]
    • \w vs [a-zA-Z]
    • \D vs ^[a-zA-Z]
  • Capture Groups
    • Use parentheses around multiple tokesn to group them together, similar to math
    • /Greg(ory)?/i matches greg and gregory
    • Probably not included in the game
      • Backreferences \1Used to repeat the previous pattern
      • Named groups
        • (?<mygroup>[abc])=\k<mygroup> same as ([abc])=\1

Pratice Tasks & Challenges

AKA: Applying the knowledge

  • Match every version of hello except the last
    • q: hello helllllllo helllo helo
    • a: /hel{2,6}o/
  • Match only the digits
    • q: abc123xyz
    • a: /\d/ or /[1-3]/
  • Match everything except last string
    • q: bird. mouse. house
    • a: /.*\./
  • Match every other word (requires array of strings with three or more words)
  • Remove repeating characters
  • Match valid .com web addresses
    • ^(http|https):\/\/+[\www\d]+\.[\w]+(\/[\w\d]+)?
  • Remove comma from number
  • Match all zeros
  • Match these email addresses (stacked enemies?)
  • Match these phone numbers (stacked?)
  • English & British spelling
  • Matching the hard way (with easy characters locked)

Real World Use Cases

AKA: What regex can do for you

  • Optional Characters (match alternate spellings)
    • neighbo?ur
    • apologize || apologise
    • Jan(uary)?
    • {3}(.)?
  • Match email addresses
    • /[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,4}/
    • /^.+@.+$/
  • Format phone numbers
    • /((\<1[\-\. ])?(\(|\<)\d\d\d[\)\.\-/ ] ?)?\<\d\d\d[\.\- ]\d\d\d\d\>/
  • SSN
    • /\<\d\d\d[\- ]\d\d[\- ]\d\d\d\d\>/
  • Remove comma from number
    • TBD
  • Find HTML tag
    • <([A-Z][A-Z0-9]*)\b[^>]*>(.*?)</\1>
    • <title>(.*)</title>
  • Trimming whitespace
    • ^[ \t]+|[ \t]+$
    • [ \t\r\n]
  • Matching valid date
    • ^(19|20)\d\d([- /.])(0[1-9]|1[012])\2(0[1-9]|[12][0-9]|3[01])$
  • Credit card numbers
    • /\<((\d\d\d\d)[\- ]){3}\d\d\d\d\>/
  • Find or format currency [$ and 2 decimals]
    • ^[+-]?[0-9]{1,3}(?:,?[0-9]{3})*\.[0-9]{2}$