What is Regex?
Usually called with Regular Expression , Regexp, or Regex. Regex is a string of text that allows you to create patterns that help match, locate, and manage text.
Regular expressions are a generalized way to match patterns with sequences of characters. It is used in every programming language like C++, Java, Python, Javascript, etc.
Why do we need to use Regex, ok before Regex is very applicable in Front End and Back End.
Regex is useful for filtering text, this is very useful because by using Regex we can choose what characters can enter our server and with regex, we can also filter out a file extension and many more. Ok for more convenience let's do it in this tutorial.
Ok in the introduction in this tutorial we will implement regex using modern javascript using ES6 +.
Ok Before starting this tutorial you can invite your pet like your cat or dog. To walk on your keyboard. LOL.
1. Regex For Number
const regNumber = /^\d*(\.\d+)?$/
const result = '123'.match(regNumber) // true
if (result) {
console.log('Match')
} else {
console.log('Not Match')
}
2. Regex For Match Lowercase
const regexStringSensitive = /[a-z]/g
const result = 'HELLO'.match(regexStringSensitive)
if (result) {
console.log('True')
} else {
console.log('False')
}
3. Regex For Match Email
const regexEmail = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/
const result = 'helo@gmail.com'.match(regexEmail)
if (result) {
console.log('Email is Match')
} else {
console.log('Not Match')
}
4. Regex For Match Some String
const regexMatchString = /(abc|def)[0-9]{8,11}/
const result = 'abc234832748374asdf7943278934haskhjd'.match(regexMatchString) //if match abc234832748374 it will true
if (result) {
console.log('Match')
} else {
console.log('Not Match')
}
5. Regex For Match Multi-Word
const regexMatchLove = /\LOVE|\bLie/
const result = 'I LOVE YOU AND I NOT LIE'.match(regexMatchLove) // Match with word LOVE and LIE
if (result) {
console.log('Match Word')
} else {
console.log('Not Match')
}
6. Regex For Match File Extensions
const regexFileName = /\.(gif|jpg|jpeg|tiff|png)$/i
const result = 'helo.jpg'.match(regexFileName) // match with filename gif|jpg|jpeg|tiff|png
if (result) {
console.log('Match File')
} else {
console.log('Not Match')
}
7. Regex Min Max
const regexMinMax = /^.{8,20}$/
const result = 'helo.jpg 123'.match(regexMinMax) //min 8 max 20
if (result) {
console.log('Recomended Password')
} else {
console.log('Not Recomended Password')
}
8. Regex For Special Character
const regexSpecialCharacter = /[\!\@\#\$\%\^\&\*\)\(\+\=\.\<\>\{\}\[\]\:\;\'\"\|\~\`\_\-]/g
const result = '*( Helo {k. ='.match(regexSpecialCharacter)
if (result) {
console.log('Contain Special Character')
} else {
console.log('Not Contain Special Character')
}
Reference for Regex
Any character except [\^$.|?*+() Literal character
\ followed by any of [\^$.|?*+(){} Backslash escapes a metacharacter
. Any character
| Alternation
\| Alternation
? Greedy quantifier
\? Greedy quantifier
?? Lazy quantifier
?+ Possessive quantifier
* Greedy quantifier
*? Lazy quantifier
*+ Possessive quantifier
+ Greedy quantifier
\+ Greedy quantifier
+? Lazy quantifier
++ Possessive quantifier
{ and } Literal curly braces
{n} where n is an integer >= 1 Fixed quantifier
{n,m} where n >= 0 and m >= n Greedy quantifier
{n,} where n >= 0 Greedy quantifier
{,m} where m >= 1 Greedy quantifier
\{n\} where n is an integer >= 1 Fixed quantifier
\{n,m\} where n >= 0 and m >= n Greedy quantifier
\{n,\} where n >= 0 Greedy quantifier
\{,m\} where m >= 1 Greedy quantifier
{n,m}? where n >= 0 and m >= n Lazy quantifier
{n,}? where n >= 0 Lazy quantifier
{,m}? where m >= 1 Lazy quantifier
{n,m}+ where n >= 0 and m >= n Possessive quantifier
{n,}+ where n >= 0 Possessive quantifier
^ String anchor
^ Line anchor
$ String anchor
$ Line anchor
\a Character escape
\A String anchor
\A Attempt anchor
\b Word boundary
\b Backspace character
\B Word non-boundary
\B Backslash character
\c XML shorthand
\ca through \cz Control character escape
\cA through \cZ Control character escape
\C XML shorthand
\d Digits shorthand
\D Non-digits shorthand
\e Escape character
\f Form feed character
\g{name} Named backreference
\g-1, \g-2, etc. Relative Backreference
\g{-1}, \g{-2}, etc. Relative Backreference
\g1 through \g99 Backreference
\g{1} through \g{99} Backreference
\g<name> where “name” is the name of a capturing group Named subroutine call
\g<name> where “name” is the name of a capturing group Named backreference
\g'name' where “name” is the name of a capturing group Named subroutine call
\g'name' where “name” is the name of a capturing group Named backreference
\g<0> Recursion
\g'0' Recursion
\g<1> where 1 is the number of a capturing group Subroutine call
\g<1> where 1 is the number of a capturing group Backreference
\g'1' where 1 is the number of a capturing group Subroutine call
\g'1' where 1 is the number of a capturing group Backreference
\g<-1> where -1 is a negative integer Relative subroutine call
\g<-1> where -1 is a negative integer Relative backreference
\g'-1' where -1 is a negative integer Relative subroutine call
\g'-1' where -1 is a negative integer Relative backreference
\g<+1> where +1 is a positive integer Forward subroutine call
\g'+1' where +1 is a positive integer Forward subroutine call
\G Attempt anchor
\G Match anchor
\h Hexadecimal digit shorthand
\h Horizontal whitespace shorthand
\H Non-hexadecimal digit shorthand
\H Non-horizontal whitespace shorthand
\i XML shorthand
\I XML shorthand
\k<name> Named backreference
\k'name' through \k'99' Named backreference
\k{name} Named backreference
\k<1> through \k<99> Backreference
\k'1' through \k'99' Backreference
\k<-1>, \k<-2>, etc. Relative Backreference
\k'-1', \k'-2', etc. Relative Backreference
\K Keep text out of the regex match
\l Lowercase shorthand
\L Non-lowercase shorthand
\m Tcl start of word boundary
\M Tcl end of word boundary
\n Line feed character
\N Not a line break
Literal CRLF, LF, or CR line break Line break
\o{7777} where 7777 is any octal number Octal escape
\pL where L is a Unicode category Unicode category
\PL where L is a Unicode category Unicode category
\p{L} where L is a Unicode category Unicode category
\p{IsL} where L is a Unicode category Unicode category
\p{Category} Unicode category
\p{IsCategory} Unicode category
\p{Script} Unicode script
\p{IsScript} Unicode script
\p{Block} Unicode block
\p{InBlock} Unicode block
\p{IsBlock} Unicode block
\P{Property} Negated Unicode property
\p{^Property} Negated Unicode property
\P{^Property} Unicode property
\Q…\E Escape sequence
\r Carriage return character
\R Line break
\s Whitespace shorthand
\S Non-whitespace shorthand
\t Tab character
\u Uppercase shorthand
\uFFFF where FFFF are 4 hexadecimal digits Unicode code point
\u{FFFF} where FFFF are 1 to 4 hexadecimal digits Unicode code point
\U Non-uppercase shorthand
\v Vertical tab character
\v Vertical whitespace shorthand
\V Non-vertical whitespace shorthand
\w Word character shorthand
\W Non-word character shorthand
\xFF where FF are 2 hexadecimal digits Hexadecimal escape
\xFFFF where FFFF are 4 hexadecimal digits Unicode code point
\x{FFFF} where FFFF are 1 to 4 hexadecimal digits Unicode code point
\X Unicode grapheme
\y Tcl word boundary
\Y Tcl word non-boundary
\Z String anchor
\z String anchor
\0 NULL escape
\1 through \7 Octal escape
\1 through \9 Backreference
\10 through \77 Octal escape
\10 through \99 Backreference
\100 through \377 Octal escape
\01 through \0377 Octal escape
\‘ String anchor
\‘ Attempt anchor
\' String anchor
\< GNU word boundary
\> GNU word boundary
[[:<:]] POSIX word boundary
[[:>:]] POSIX word boundary
(regex) Capturing group
\(regex\) Capturing group
(?:regex) Non-capturing group
(?<name>regex) Named capturing group
(?'name'regex) Named capturing group
(?#comment) Comment
(?|regex) Branch reset group
(?>regex) Atomic group
(?=regex) Positive lookahead
(?!regex) Negative lookahead
(?<=regex) Positive lookbehind
(?<!regex) Negative lookbehind
(?(?=regex)then|else) where (?=regex) is any valid lookaround and then and else are any valid regexes Lookaround conditional
(?(regex)then|else) where regex, then, and else are any valid regexes and regex is not the name of a capturing group Implicit lookahead conditional
(?(name)then|else) where name is the name of a capturing group and then and else are any valid regexes Named conditional
(?(<name>)then|else) where name is the name of a capturing group and then and else are any valid regexes Named conditional
(?('name')then|else) where name is the name of a capturing group and then and else are any valid regexes Named conditional
(?(1)then|else) where 1 is the number of a capturing group and then and else are any valid regexes Conditional
(?(-1)then|else) where -1 is a negative integer and then and else are any valid regexes Relative conditional
(?(+1)then|else) where +1 is a positive integer and then and else are any valid regexes Forward conditional
(?(+1)then|else) where 1 is the number of a capturing group and then and else are any valid regexes Conditional
(?<capture-subtract>regex) where “capture” and “subtract” are group names and “regex” is any regex Balancing group
(?'capture-subtract'regex) where “capture” and “subtract” are group names and “regex” is any regex Balancing group
(?&name) where “name” is the name of a capturing group Named subroutine call
(?(DEFINE)regex) where “regex” is any regex Subroutine definitions
(?P<name>regex) Named capturing group
(?P=name) Named backreference
(?P=1) through (?P=99) Backreference
(?P>name) where “name” is the name of a capturing group Named subroutine call
(?R) Recursion
(?0) Recursion
(?1) where 1 is the number of a capturing group Subroutine call
(?-1) where -1 is a negative integer Relative subroutine call
(?+1) where +1 is a positive integer Forward subroutine call
Now that above is the Regular Expression that is most widely used by programmers to filter characters. Please develop it with your needs. It may be useful.
source: www.regular-expressions.info
Top comments (3)
Although regex is cool, but please try to avoid it where possible. It’s okay for single task but may affect site performance for complex tasks.
For example, your
/^.{8,20}$/pattern is used to check the length of a string. You can do this instead:If you have to, then make sure to do a minimum validation check with less effort before doing the regex part. So, at least if your value does not pass the first check, it will then abort the later checks:
JavaScript might not the case but PHP and other templating language performance can be decreased by regular expression and so they can be improved this way.
Thank you Bro, yes you can use length, but this is a regex tutorial. Thank you for the advice and discussion.
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