Regular Expressions (RegEx) – Quick Reference
Regular expression also known as regex is a sequence of characters/symbols that forms a search pattern. It is supported by most programming language including Perl, Javascript, PHP, C-Sharp and Java.
Commonly Used Symbols and Syntax
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META CHARACTERS
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^
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Start of subject (or line in multiline mode) |
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$
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End of subject (or line in multiline mode) |
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[
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Start character class definition |
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]
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End character class definition |
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Alternates ( a|b matches a or b ) |
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(
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Start subpattern |
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)
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End subpattern |
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Escape character |
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BASE CHARACTER CLASSES
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w
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Any “word” character (a-z 0-9 _) |
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W
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Any non-“word” character |
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s
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Whitespace (space, tab, CRLF) |
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S
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Any non-whitespace character |
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d
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Digits (0-9) |
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D
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Any non-digit character |
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.
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Any character except newline |
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QUANTIFIERS
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*
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Zero or more |
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+
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One or more |
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?
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Zero or one occurrence |
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{n}
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n occurrences exactly |
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{n,}
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At least n occurrences |
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{,m}
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At most m occurrences |
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{n,m}
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Between n and m occurrences inclusive |
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[…]
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list or range of characters (or both). [abc] means “any single character that is either a, b or c” |
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[^…]
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any single character that is not in the class. [^0-9xyz] matches any single character that isn’t a digit and isn’t the letter x, y, or z |
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r
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escape sequences r (carriage return) |
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t
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escape sequences t (tab) |
These are most of the commonly-used RegEx features, there are quite a few others
you may want to explore. The complete manual is at www.pcre.org/pcre.txt
USEFUL REGULAR EXPRESSIONS
Here’s a list of some useful regular expressions that can make life as a
developer less hassling.
Regular expression for username
Following pattern will match alphanumeric string including “_” of length 3 to 25.
^[a-z0-9_]{3,25}$Regular expression for email
^[a-z0-9]+([_a-z0-9.-]+)*[a-z0-9]+@[a-z0-9-]+(.[a-z0-9-]+)*(.[a-z]{2,4})$Regular expression for Password
Password must contain letters a-zA-Z and at least one digit 0-9
(/^(?=.*d)(?=.*[a-z])(?=.*[A-Z])[0-9a-zA-Z]{8,}$/)Explanation…
(/^(?=.*d) //should contain at least one digit
(?=.*[a-z]) //should contain at least one lower case
(?=.*[A-Z]) //should contain at least one upper case
[a-zA-Z0-9]{8,} //should contain at least 8 from the mentioned characters $/)Regular expression for URL
^http[s]?://[a-z0-9-.]+.[a-z.]{2,5}(/[a-z0-9%-_.?=&@#]*)?$Regular expression for Decimal value
^[0-9]+$Regular expression for Float value
^[0-9]*.[0-9]*[1-9]+$Regular expression for Removing Whitespaces
str.replace(/^s+|s+$|s+(?=s)/g, "")Share your favorite RegEX using the comment form below…
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Thanks for the password guidance here. We’ve got a client asking to improve the password security on the site through stronger passwords and I was stumbling a bit in terms of getting the syntax for a clean run. This is working perfectly!
Getting better password security is very important! I have been working all morning on trying to figure out how to complete the code. Your tips helped me a great deal, thanks!
Password security is very important, I agree, but when coding a site you should realize that you cannot control everything the user does. They should provide good, long, complex passwords to begin with.