+
-
+
-Above regular expression can accepts the strings `john_doe`, `jo-hn\_doe` and `john12\_as`. It does not match `Jo` because that string
+Above regular expression can accept the strings `john_doe`, `jo-hn\_doe` and `john12\_as`. It does not match `Jo` because that string
contains uppercase letter and also it is too short.
## Table of Contents
@@ -41,7 +41,7 @@ contains uppercase letter and also it is too short.
- [Caret](#281-caret)
- [Dollar](#282-dollar)
- [Shorthand Character Sets](#3-shorthand-character-sets)
-- [Lookaround](#4-ookaround)
+- [Lookaround](#4-lookaround)
- [Positive Lookahead](#41-positive-lookahead)
- [Negative Lookahead](#42-negative-lookahead)
- [Positive Lookbehind](#43-positive-lookbehind)
@@ -110,10 +110,17 @@ expression `[Tt]he` means: an uppercase `T` or lowercase `t`, followed by the le
"[Tt]he" => The car parked in the garage.
+<<<<<<< HEAD
Just like above example the regular expression `ge[.]` means: a lowercase character `g`, followed by letter `e`, followed by `.` character.
"ge[.]" => The car parked in the garage. +======= +A period inside a character set, however, means a literal period. The regular expression `ar[.]` means: a lowercase character `a`, followed by letter `r`, followed by a period. + ++"ar[.]" => A garage is a good place to park a car. +>>>>>>> 7cac291415345a24a7bf1db02b6612576aab0446### 2.2.1 Negated character set @@ -139,7 +146,7 @@ of preceding lowercase character `a`. But if it appears after a character set or character set. For example the regular expression `[a-z]*` means: any number of lowercase letters in a row.-"[a-z]*" => The car parked in the garage #21. +"[a-z]*" => The car parked in the garage #21.The `*` symbol can be used with the meta character `.` to match any string of characters `.*`. The `*` symbol can be used with the @@ -180,7 +187,7 @@ character can be repeated. For example the regular expression `[0-9]{2,3}` means characters in the range of 0 to 9).-"[0-9]{2}" => The number was 9.9997 but we rounded it off to 10.0. +"[0-9]{2,3}" => The number was 9.9997 but we rounded it off to 10.0.We can leave out the second number. For example the regular expression `[0-9]{2,}` means: Match 2 or more digits. If we also remove @@ -232,7 +239,7 @@ expression `(f|c|m)at\.?` means: lowercase letter `f`, `c` or `m`, followed by l ## 2.8 Anchors -In regular expression to check if the matching symbol is the starting symbol or endnig symbol of the input string for this purpose +In regular expression to check if the matching symbol is the starting symbol or ending symbol of the input string for this purpose we use anchors. Anchors are of two types: First type is Caret `^` that check if the matching character is the start character of the input and the second type is Dollar `$` that checks if matching character is the last character of the input string. @@ -342,7 +349,7 @@ are after not after the word `The` or `the`. ## 5. Flags -Flags are also called modifiers because they modifies the output of a regular expression. These flags can be used in any order or +Flags are also called modifiers because they modify the output of a regular expression. These flags can be used in any order or combination, and are an integral part of the RegExp. |Flag|Description| @@ -387,9 +394,9 @@ string. ### 5.3 Multiline The `m` modifier is used to perform a multi line match. As we discussed earlier anchors `(^, $)` are used to check if pattern is -the beginning of the input or end fo the input string. But if we want that anchors works on each line we use `m` flag. For example the +the beginning of the input or end of the input string. But if we want that anchors works on each line we use `m` flag. For example the regular expression `/at(.)?$/gm` means: lowercase character `a`, followed by lowercase character `t`, optionally anything except new -line. And beacause of `m` flag now regular expression engine matches pattern at the end of each line in a string. +line. And because of `m` flag now regular expression engine matches pattern at the end of each line in a string."/.at(.)?$/" => The fat @@ -407,15 +414,15 @@ line. And beacause of `m` flag now regular expression engine matches pattern at * *Positive Integers*: `^\d+$` * *Negative Integers*: `^-\d+$` -* *Phone Number*: `^+?[\d\s]{3,}$` -* *Phone with code*: `^+?[\d\s]+(?[\d\s]{10,}$` +* *US Phone Number*: `^+?[\d\s]{3,}$` +* *US Phone with code*: `^+?[\d\s]+(?[\d\s]{10,}$` * *Integers*: `^-?\d+$` * *Username*: `^[\w\d_.]{4,16}$` * *Alpha-numeric characters*: `^[a-zA-Z0-9]*$` * *Alpha-numeric characters with spaces*: `^[a-zA-Z0-9 ]*$` * *Password*: `^(?=^.{6,}$)((?=.*[A-Za-z0-9])(?=.*[A-Z])(?=.*[a-z]))^.*$` * *email*: `^([a-zA-Z0-9._%-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4})*$` -* *IP address*: `^((?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))*$` +* *IPv4 address*: `^((?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))*$` * *Lowercase letters only*: `^([a-z])*$` * *Uppercase letters only*: `^([A-Z])*$` * *URL*: `^(((http|https|ftp):\/\/)?([[a-zA-Z0-9]\-\.])+(\.)([[a-zA-Z0-9]]){2,4}([[a-zA-Z0-9]\/+=%&_\.~?\-]*))*$` @@ -433,4 +440,4 @@ line. And beacause of `m` flag now regular expression engine matches pattern at ## License -MIT © [Zeeshan Ahmed](mailto:ziishaned@gmail.com) \ No newline at end of file +MIT © [Zeeshan Ahmed](mailto:ziishaned@gmail.com)