Regular Expressions - Cheat Sheet

Regular Expressions/Published-Topics.md

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+bharat soni

Regular Expressions/Regular Expressions - Cheat Sheet.md

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+# Regular Expressions - Cheat Sheet
+
+* use a single `|` to say 'or'
+* `[ ]` - says any of the characters inside the brackets
+* `?` make the preceding token optional
+* `.+` - matches all characters to the end of the line
+* use parentheses to group characters as using the `|` alone divide the regex into only a left and right side.
+* `^` matches only if it's at the beginning of a string
+* `$` matches only if it's the end of a string
+* `+` is greedy - it won't just get the next token. it will keep searching until it reaches the last one.
+* `+?` is not greedy - it will just search to the next occurrence of a token.
+* `{3}` - would match 3 occurrences of the preceding token
+* `{3,4}` - could match the range of 3 to 4 characters of the preceding token
+
+## Flags
+* `\w` - matches any word character
+* `\r` = carriage return
+* `\n` = new lines
+* `\s` = space characters
+* `\w` = word character
+* `\d` = digits 0-9
+
+## Lookahead and Lookbehind
+* `(?<!`  = negative look behind
+* `(?<=`  = positive look behind
+* `(?=`  = positive look ahead 
+* `(?!`  = negative look ahead
+
+## JavaScript Methods
+* `RegExp.exec(string)` = Applies the RegExp to the given string, and returns the match information.
+* `RegExp.test(string)` = Tests if the given string matches the Regexp, and returns true if matching, false if not.
+* `String.match(pattern)` = Matches given string with the RegExp. With g flag returns an array containing the matches, without g flag returns just the first match or if no match is found returns null.
+* `String.search(pattern)` = Matches RegExp with string and returns the index of the beginning of the match if found, -1 if not.
+* `String.replace(pattern,string)` = Replaces matches with the given string, and returns the edited string.
+* `String.split(pattern)` = Cuts a string into an array, making cuts at matches.