Quick Reference

    [abc] A single character: a, b or c
    [^abc] Any single character but a, b, or c
    [a-z] Any single character in the range a-z
    [a-zA-Z] Any single character in the range a-z or A-Z
    ^ Start of line
    $ End of line
    \A Start of string
    \z End of string
    . Any single character
    \s Any whitespace character
    \S Any non-whitespace character
    \d Any digit
    \D Any non-digit
    \w Any word character (letter, number, underscore)
    \W Any non-word character
    \b Any word boundary character
    (...) Capture everything enclosed
    (a|b) a or b
    a? Zero or one of a
    a* Zero or more of a
    a+ One or more of a
    a{3} Exactly 3 of a
    a{3,} 3 or more of a
    a{3,6} Between 3 and 6 of a

    options: i case insensitive; m make dot match newlines; x ignore whitespace in regex; o perform #{...} substitutions only once