Regular Expressions 101

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Community Patterns

1

scam_4

PCRE2 (PHP >=7.3)
In an HTML page, replace the text micro with µ. Oh, and don't screw up the code: don't replace inside or &entities;
Submitted by anonymous - 3 months ago
1

scam_20

PCRE2 (PHP >=7.3)
Validate a line in quotes. Return one (and only one) backreference with the text. ie: quoted text from "quoted text". Note: a \ escapes any char, so \" is a valid escape.
Submitted by anonymous - 3 months ago
1

scam_19

PCRE2 (PHP >=7.3)
Use substitution to put commas in all numbers to separate the thousands. ie: 12345678 → 12,345,678. The number could be in a sentence, and there may be more than one number in the sentence.
Submitted by anonymous - 3 months ago
1

scam_18

PCRE2 (PHP >=7.3)
Replace every other character if it's a \d with * (only those in even positions: 2, 4, 6, etc). Example: a1b2cde3g45hi6 should become abcdeg4hi6
Submitted by anonymous - 3 months ago
1

Validating IP V4

PCRE2 (PHP >=7.3)
VALIDATING IP V4 1.1.1.1 2.2.2.2 3.3.3.3 4.4.4.4 5.5.5.5...
Submitted by An0nym0us - 3 months ago
1

Test

PCRE2 (PHP >=7.3)
This is a test
Submitted by anonymous - 3 months ago
1

Quiz_9_Match_An_Email

PCRE2 (PHP >=7.3)
Verify that a given e-mail address is valid. We all know how complex emails are, but despite this, let's give it a try and see what we can come up with. You could start by trying to match contact@regex101.com (denoted as @.).
Submitted by anonymous - 3 months ago
1

Quiz_10_Followed_by_#

PCRE2 (PHP >=7.3)
For every occurrence of the char #, match the previous character and save it in a group (backreference). Example: for the text "a#bc# -#", set backreferences with a, c and -. You are not allowed to consume the hash character.
Submitted by anonymous - 3 months ago
1

Quiz_11_Validate_Floating_Point_Number

PCRE2 (PHP >=7.3)
Check if a floating point number (e.g. 3.14159) is in a valid format.
Submitted by anonymous - 3 months ago
1

Quiz_8_HTML_Tags

PCRE2 (PHP >=7.3)
Strip all HTML tags from a string. HTML tags are enclosed in . The regex will be applied on a line-by-line basis, meaning partial tags will need to be handled by the regex. Don't worry about opening or closing tags; we just want to get rid of them all. Note: This task is meant to be a learning exe...
Submitted by anonymous - 3 months ago
2

Quiz_12_Match_Any_Number_Between_0-100

PCRE2 (PHP >=7.3)
Could you help me validate my input and only match positive integers between the range of 0 and 100? There can be several numbers in a string which I would want to retrieve. Try out these example strings: ...
Submitted by anonymous - 3 months ago
1

Quiz_7_Validate_An_IP

PCRE2 (PHP >=7.3)
Validate an IPv4 address. The addresses are four numbered separated by three dots, and can only have a maximum value of 255 in either octet. Start by trying to validate 172.16.254.1.
Submitted by anonymous - 3 months ago
2

Quiz_13_Match_Alternating_0s_And_1s_In_Any_Order

PCRE2 (PHP >=7.3)
I'm trying to match bit sequences which are alternating between 1 and 0 and never have more than one 1 or 0 in a row. They can be single digits. Try matching this: 0101010, 1010101010 or 1
Submitted by anonymous - 3 months ago
1

Quiz_6_Broken_Keyboard

PCRE2 (PHP >=7.3)
Oh no! It seems my friends spilled beer all over my keyboard last night and my keys are super sticky now. Some of the time whennn I press a key, I get two duplicates. Can you ppplease help me fix thhhis? Substitute with $1
Submitted by anonymous - 3 months ago
2

Quiz_14_Spam_filter

PCRE2 (PHP >=7.3)
Match a string that contains any of the following substrings: http://, www., porn, or credit card. But don't match the text if it contains one of: not allowed, filter, or mirc. Don't use word boundaries (anywhere in the text is fine). If you need help, try reading this.
Submitted by anonymous - 3 months ago
1

Quiz_5_Whitespace

PCRE2 (PHP >=7.3)
Find all occurrences of 4 or more whitespace characters in a row throughout the string.
Submitted by anonymous - 3 months ago
2

Quiz_15_Not_surrounded_by_digits

PCRE2 (PHP >=7.3)
Replace every . (dot) with a - (hyphen) except when the dot is surrounded by digits. E.g.: .a.b.1.2. should become -a-b-1.2-
Submitted by anonymous - 3 months ago
1

Quiz_4_Retrieve_Numbers

PCRE2 (PHP >=7.3)
Count the number of integers in a given string. Integers are, for example: 1, 2, 65, 2579, etc.
Submitted by anonymous - 3 months ago
2

Quiz_16_Repeated_Words

PCRE2 (PHP >=7.3)
I'd like to know if a text contains words with 4 characters or more which are repeated 3 or more times in the text (anywhere in the text). If so, set one (and only one) backreference for each word.
Submitted by anonymous - 3 months ago
1

Quiz_3_Uppercase_Consonants

PCRE2 (PHP >=7.3)
With regex you can count the number of matches. Can you make it return the number of uppercase consonants (B,C,D,F,..,X,Y,Z) in a given string? E.g.: it should return 3 with the text ABcDeFO!. Note: Only ASCII. We consider Y to be a consonant! Example: the regex /./g will return 3 when run against ...
Submitted by anonymous - 3 months ago
1...34567...902

Community Library Entry

0

Regular Expression
PCRE (PHP <7.3)

/
\b (?!\p{Lu}+\b) # CaMeL can't be an ALLCAPS (remove to allow) (?=\p{L}*\p{Ll}) # CaMeL word should have at least 1 lowercase letter (?=\p{L}*\p{Lu}) # CaMeL word should have at least 1 uppercase letter (?!\p{Lu}\p{Ll}*\b) # CaMeL word can't be `Xxxx` or `X` \p{L}+ # CaMeL word should contain at least 1 letter \b
/
gx
Open regex in editor

Description

The PCRE (or any regex flavor supporting word boundaries, Unicode properties and lookaheads) \b(?!\p{Lu}+\b)(?=\p{L}\p{Ll})(?=\p{L}\p{Lu})(?!\p{Lu}\p{Ll}*\b)\p{L}+\b regex finds CaMeL words that:

  • Have at least 1 lowercase letter
  • Have at least 1 uppercase letter
  • Do not follow the X, XXX or Xxxx patterns

Author's SO profile: http://stackoverflow.com/users/3832970/wiktor-stribi%C5%BCew

Submitted by Wiktor Stribiżew - 9 years ago