Regular Expressions

Basic Rules

• \d match one number
• \w match one letter or one number
• \s match one space (also include tab)
• . match any symbol
• * match any number of symbols (include zero)
• + match at least one symbol
• ? match one or none symbol
• {n} means n symbols
• {n,m} means n to m symbols

Advanced Rules

• [] can be used to indicate range
  • [0-9a-zA-Z\_] matches one number or letter or underscore
  • [0-9a-zA-Z\_]+ matches one string containing at least one number, letter or underscore.
  • [a-zA-Z\_][0-9a-zA-Z\_]* matches any string starting with letter or underscore followed by any number of number/letter/underscore
  • [a-zA-Z\_][0-9a-zA-Z\_]{0,19} specify the length of the string
• A|B match A or B
• ^ means the header
• $ means the end