Dmitry Kalashnikov

Regular expressions (regex) let you search for a particular pattern. Regex consist of literal characters, and special characters, also called meta characters. Regex syntax has 2 modes, one inside of character classes, which is inside [ ] and one outsided of character classes.

Character classes []:  Regex inside [] are in different mode and have different syntax. It matches a  single character specified as a list, range or class shortcut.  03[-./]19[-./]76  Will match the above date delimited by a dot or a hyphen.  Inside [] the dot is no longer a meta-character, its matched literally!  Negation Operator ^  f[^u]  matches something with f, followed by any character other then u  Character classes shortcuts  \d [0-9] digit  \D non digit  \w [a-zA-Z0-9_] part of word  \W non word  \s [ \t\n\r\f\v] whitespace  \S non whitespaceAlternation:  | operator is ‘or’  Jeff(re|er|izz)y  => Jeffrey, Jeffery, JeffizzyConditionals:  (?if then | else)  if the “if” part is true, “then” expression is attmpted, otherwise  “else” is attempted  (?if then)  else condition is optional, so is the pipe character prefixing itAnchors:  ^  beg of line  $  end of line  \b word boundary  \B non-word boundary  Ruby:  \A begining of a string  \Z end of string (or before newline at the end)  \z end of stringOptional Items:  ? optionally matches a character before it, or you can specify a group() of  characters before it:  colou?r  will match color and colour  4(th)?  will match 4 and 4thRepetitions:  +            s1 or more times  *            0 or more times  ?            1 or 0 times  {n}          match exactly n times  {min, max}   min to max times  {min,}       at least min  {,max}       at most max (ruby)Backreferences:  First matched group ():    sed, vi: \1    ruby: $1    php: $m[1]    python, java: m.group(1)    c#: m.Groups[1]  Group zero is typically the entire matchEscape:  \. will escape dot meta characterMore Info:  http://www.regular-expressions.info/