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25+ useful and commonly used Regular Expressions

devto 2026-08-15 원문 보기 ↗

Regular Expressions (Regex) are expressions that define a search pattern. Regex can be implemented in various tasks including searching, replacing, validation and text processing/parsing. It is mostly known in the combination with the programming language Perl, but Regex are also supported by most other languages.

If you every want to really dive deep into the world of Regular Expressions, I'd recommend the book "Mastering Regular Expressions " by Jeffrey E.F. Friedl.

Testing your regular expressions

There are times in which you can't test your Regex while programming. Or you might just want to play around and test your Regex.
In any case, there are a few Regex tester online, where you can add sample data and build or test your regex. Some of them are:

Commonly used

Digits

Whole numbers:

/^\\d+$/

Decimal numbers:

/^\\d*\\.\\d+$/

Whole and decimal numbers:

/^\\d*(\\.\\d+)?$/

Negative or positive whole and decimal numbers:

/^-?\\d*(\\.\\d+)?$/

Alphanumeric

Without space

/^[a-zA-Z0-9]*$/

With Space

/^[a-zA-Z0-9 ]*$/

Username

Alphanumeric lowercase username that might contain

and a length of 3-16 characters

/^[a-z0-9_-]{3,16}$/

Email

Common email 

/^([a-zA-Z0-9._%-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,6})*$/

Uncommon email

e.g. mail@sub.provider.com

/^([a-z0-9_\\.\\+-]+)@([\\da-z\\.-]+)\\.([a-z\\.]{2,6})$/

RFC 5322 

/(?(DEFINE)
    (?<addr_spec> (?&local_part) @ (?&domain) )
    (?<local_part> (?&dot_atom) | (?&quoted_string) | (?&obs_local_part) )
    (?<domain> (?&dot_atom) | (?&domain_literal) | (?&obs_domain) )
    (?<domain_literal> (?&CFWS)? \\[ (?: (?&FWS)? (?&dtext) )* (?&FWS)? \\] (?&CFWS)? )
    (?<dtext> [\\x21-\\x5a] | [\\x5e-\\x7e] | (?&obs_dtext) )
    (?<quoted_pair> \\\\ (?: (?&VCHAR) | (?&WSP) ) | (?&obs_qp) )
    (?<dot_atom> (?&CFWS)? (?&dot_atom_text) (?&CFWS)? )
    (?<dot_atom_text> (?&atext) (?: \\. (?&atext) )* )
    (?<atext> [a-zA-Z0-9!#$%&'*+\\/=?^_`{|}~-]+ )
    (?<atom> (?&CFWS)? (?&atext) (?&CFWS)? )
    (?<word> (?&atom) | (?&quoted_string) )
    (?<quoted_string> (?&CFWS)? " (?: (?&FWS)? (?&qcontent) )* (?&FWS)? " (?&CFWS)? )
    (?<qcontent> (?&qtext) | (?&quoted_pair) )
    (?<qtext> \\x21 | [\\x23-\\x5b] | [\\x5d-\\x7e] | (?&obs_qtext) )
    # comments and whitespace
    (?<FWS> (?: (?&WSP)* \\r\\n )? (?&WSP)+ | (?&obs_FWS) )
    (?<CFWS> (?: (?&FWS)? (?&comment) )+ (?&FWS)? | (?&FWS) )
    (?<comment> \\( (?: (?&FWS)? (?&ccontent) )* (?&FWS)? \\) )
    (?<ccontent> (?&ctext) | (?&quoted_pair) | (?&comment) )
    (?<ctext> [\\x21-\\x27] | [\\x2a-\\x5b] | [\\x5d-\\x7e] | (?&obs_ctext) )
    # obsolete tokens
    (?<obs_domain> (?&atom) (?: \\. (?&atom) )* )
    (?<obs_local_part> (?&word) (?: \\. (?&word) )* )
    (?<obs_dtext> (?&obs_NO_WS_CTL) | (?&quoted_pair) )
    (?<obs_qp> \\\\ (?: \\x00 | (?&obs_NO_WS_CTL) | \\n | \\r ) )
    (?<obs_FWS> (?&WSP)+ (?: \\r\\n (?&WSP)+ )* )
    (?<obs_ctext> (?&obs_NO_WS_CTL) )
    (?<obs_qtext> (?&obs_NO_WS_CTL) )
    (?<obs_NO_WS_CTL> [\\x01-\\x08] | \\x0b | \\x0c | [\\x0e-\\x1f] | \\x7f )
    # character class definitions
    (?<VCHAR> [\\x21-\\x7E] )
    (?<WSP> [ \\t] )
)
^(?&addr_spec)$/xmg

Passwords

Moderate Password

Password with at least

and a minimum length of 8 characters.

Spaces allowed.

/(?=(.*[0-9]))((?=.*[A-Za-z0-9])(?=.*[A-Z])(?=.*[a-z]))^.{8,}$/

Spaces not allowed.

/^((?=\\S*?[A-Z])(?=\\S*?[a-z])(?=\\S*?[0-9]).{8,})\\S$/

With optional special character and spaces not allowed

/^(?=.*\\d)(?=.*[a-zA-Z])[0-9a-zA-Z$&+,:;=?@#|'<>.-^*()%!]{8,}$/

Strong Password

Passwords with at least

and a minimum of 8 characters with spaces not allowed.

All special characters

/^(?=.*\\d)(?=.*[A-Z])(?=.*[a-z])(?=.*[^\\w\\d\\s:])([^\\s]){8,}$/

One of these special characters: !@#$%^&*()-=¡£+~.,<>/?;:'"|[]{}_

/^(?=.*\\d)(?=.*[A-Z])(?=.*[a-z])(?=.*[\\!\\@\\#\\$\\%\\^\\&\\*\\(\\)\\-\\=\\¡\\£\\_\\+\\~\\.\\,\\<\\>\\/\\?\\;\\:\\'\\"\\\\\\|\\[\\]\\{\\}])([^\\s]){8,}$/

Strong+ Password

Password with minimum

and does not contain certain words.

^(?=.*\\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[^\\w\\s\\d:])(?=(?:([\\w\\d])\\1?(?!\\1\\1)))(?!(?=.*([Jj]ohn|[Dd]oe]|blabla))).{12,}$

IP addresses

IPv4 

/^(?:(?:25[0-5]|2[0-4]\\d|1?\\d?\\d)(?:\\.(?!$)|$)){4}$/

Private IPv4

/^(10(\\.(1?\\d\\d?|2([0-4]\\d?|5[0-5])))(?2)|172\\.(1[6-9]|2\\d|3[0-2])(?2)|192\\.168(?2))(?2)$/

IPv6 

/(?:(?:(?:[A-F0-9]{1,4}:){6}|(?=(?:[A-F0-9]{0,4}:){0,6}(?:[0-9]{1,3}\\.){3}[0-9]{1,3}(?![:.\\w]))(([0-9A-F]{1,4}:){0,5}|:)((:[0-9A-F]{1,4}){1,5}:|:)|::(?:[A-F0-9]{1,4}:){5})(?:(?:25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|(?:[A-F0-9]{1,4}:){7}[A-F0-9]{1,4}|(?=(?:[A-F0-9]{0,4}:){0,7}[A-F0-9]{0,4}(?![:.\\w]))(([0-9A-F]{1,4}:){1,7}|:)((:[0-9A-F]{1,4}){1,7}|:)|(?:[A-F0-9]{1,4}:){7}:|:(:[A-F0-9]{1,4}){7})(?![:.\\w])/i

With Subnet

/(?:(?:(?:[A-F0-9]{1,4}:){6}|(?=(?:[A-F0-9]{0,4}:){0,6}(?:[0-9]{1,3}\\.){3}[0-9]{1,3}(?![:.\\w]))(([0-9A-F]{1,4}:){0,5}|:)((:[0-9A-F]{1,4}){1,5}:|:)|::(?:[A-F0-9]{1,4}:){5})(?:(?:25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|(?:[A-F0-9]{1,4}:){7}[A-F0-9]{1,4}|(?=(?:[A-F0-9]{0,4}:){0,7}[A-F0-9]{0,4}(?![:.\\w]))(([0-9A-F]{1,4}:){1,7}|:)((:[0-9A-F]{1,4}){1,7}|:)|(?:[A-F0-9]{1,4}:){7}:|:(:[A-F0-9]{1,4}){7})(?![:.\\w])\\/(?:12[0-8]|1[01][0-9]|[1-9]?[0-9])/i

IPv4 or IPv6 

/((^\\s*((([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]))\\s*$)|(^\\s*((([0-9A-Fa-f]{1,4}:){7}([0-9A-Fa-f]{1,4}|:))|(([0-9A-Fa-f]{1,4}:){6}(:[0-9A-Fa-f]{1,4}|((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){5}(((:[0-9A-Fa-f]{1,4}){1,2})|:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){4}(((:[0-9A-Fa-f]{1,4}){1,3})|((:[0-9A-Fa-f]{1,4})?:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){3}(((:[0-9A-Fa-f]{1,4}){1,4})|((:[0-9A-Fa-f]{1,4}){0,2}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){2}(((:[0-9A-Fa-f]{1,4}){1,5})|((:[0-9A-Fa-f]{1,4}){0,3}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){1}(((:[0-9A-Fa-f]{1,4}){1,6})|((:[0-9A-Fa-f]{1,4}){0,4}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(:(((:[0-9A-Fa-f]{1,4}){1,7})|((:[0-9A-Fa-f]{1,4}){0,5}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:)))(%.+)?\\s*$))/

Domains & URLs

General Domain (up to 3rd-level-domain) 

/(?:(?:([\\w\\-]*)(?:\\.))?([\\w\\-]*))\\.(\\w*)/

With optional port:

/(?:(?:([\\w\\-]*)(?:\\.))?([\\w\\-]*))\\.(\\w*)(?:\\:(\\d*))?/

With protocol and optional port:

/(\\w*)\\:\\/\\/(?:(?:([\\w\\-]*)(?:\\.))?([\\w\\-]*))\\.(\\w*)(?:\\:(\\d*))?/

With optional protocol and port:

/(?:(\\w*)\\:\\/\\/)?(?:(?:([\\w\\-]*)(?:\\.))?([\\w\\-]*))\\.(\\w*)(?:\\:(\\d*))?/

URLs with path

Usually you'll want these to match specific protocols, therefore you can set them. In this case we'll be looking for http(s) and ftp(s). Otherwise you could also use the wildcard as in the general domain example.

/(https?|ftps?):\\/\\/([\\w_-]+(?:(?:\\.[\\w_-]+)+))([\\w.,@?^=%&:\\/~+#-]*[\\w@?^=%&\\/~+#-])/

With optional protocol:

/(?:(https?|ftps?):\\/\\/)?([\\w_-]+(?:(?:\\.[\\w_-]+)+))([\\w.,@?^=%&:\\/~+#-]*[\\w@?^=%&\\/~+#-])/

File paths

File path with filename + extension 

/((\\/|\\\\|\\/\\/|https?:\\\\\\\\|https?:\\/\\/)[a-z0-9 _@\\-^!#$%&+={}.\\/\\\\\\[\\]]+)+\\.[a-z]+$/

File path with optional filename + extension 

/^(.+)/([^/]+)$/

Filename with extension 

/^[\\w,\\s-]+\\.[A-Za-z]{3}$/

Date

YYYY/MM/DD 

/([12]\\d{3}-(0[1-9]|1[0-2])-(0[1-9]|[12]\\d|3[01]))/

DD/MM/YYYY, DD-MM-YYYY, DD.MM.YYYY 

/^(?:(?:31(\\/|-|\\.)(?:0?[13578]|1[02]))\\1|(?:(?:29|30)(\\/|-|\\.)(?:0?[1,3-9]|1[0-2])\\2))(?:(?:1[6-9]|[2-9]\\d)?\\d{2})$|^(?:29(\\/|-|\\.)0?2\\3(?:(?:(?:1[6-9]|[2-9]\\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\\d|2[0-8])(\\/|-|\\.)(?:(?:0?[1-9])|(?:1[0-2]))\\4(?:(?:1[6-9]|[2-9]\\d)?\\d{2})$/

Time

HH:MM 12-hour 

/^(0?[1-9]|1[0-2]):[0-5][0-9]$/

With meridiems (am/pm)

/((1[0-2]|0?[1-9]):([0-5][0-9]) ?([AaPp][Mm]))/

HH:MM 24-hour 

/^([0-9]|0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/

With required leading '0'

/^(0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/

With Seconds

/(?:[01]\\d|2[0123]):(?:[012345]\\d):(?:[012345]\\d)/

Other

username:password 

/[0-9A-Za-z.]+:[0-z]+/

Single .env file line 

/(?:^|^)\\s*(?:export\\s+)?([\\w.-]+)(?:\\s*=\\s*?|:\\s+?)(\\s*'(?:\\\\'|[^'])*'|\\s*\\"(?:\\\\\\"|[^\\"])*\\"|\\s*`(?:\\\\`|[^`])*`|[^#\\r\\n]+)?\\s*(?:#.*)?(?:$|$)/gm

International phone number incl. european notation 

/[+]\\d{1,2}|(00)\\d{2,4}|\\d{2})( [(]\\d{1,3}[)])?[-. \\/]?\\d{2,6}?[-. \\/]?\\d{2,15}([-. \\/]{1,3}\\d{1,5}){0,4}/

Word duplicates 

/(\\b\\w+\\b)(?=.*\\b\\1\\b)/ig

Social Security Number 

/^((?!219-09-9999|078-05-1120)(?!666|000|9\\d{2})\\d{3}-(?!00)\\d{2}-(?!0{4})\\d{4})|((?!219 09 9999|078 05 1120)(?!666|000|9\\d{2})\\d{3} (?!00)\\d{2} (?!0{4})\\d{4})|((?!219099999|078051120)(?!666|000|9\\d{2})\\d{3}(?!00)\\d{2}(?!0{4})\\d{4})$/

Html tags with optional attributes 

/<\\/?[\\w\\s]*>|<.+[\\W]>/