RegEx brief

For a complete explanation about using Regular Expressions please take a look to this great article by Jim Hollenhorst.

You can use the Expresso tool for build and test regular expressions.

Special characters:

.   Match any character except newline 
\w  Match any alphanumeric character 
\s  Match any whitespace character 
\d  Match any digit 
\b  Match the beginning or end of a word 
^   Match the beginning of the string 
$   Match the end of the string 

Repetitions:

*     Repeat any number of times 
+     Repeat one or more times 
?     Repeat zero or one time 
{n}   Repeat n times 
{n,m} Repeat at least n, but no more than m times 
{n,}  Repeat at least n times 

Ranges samples:

[aeiou]  matches any vowel
[.?!]    matches the punctuation
[a-z0-9] match any lowercase letter of the alphabet, or any digit

Negations:

\W       Match any character that is NOT alphanumeric 
\S       Match any character that is NOT whitespace 
\D       Match any character that is NOT a digit 
\B       Match a position that is NOT the beginning or end of a word 
[^x]     Match any character that is NOT x 
[^aeiou] Match any character that is NOT one of the characters aeiou 

Some samples (there are a lot of best and optimal samples on Internet, look for them or use Expresso to build them):

\b\d\d\d-\d\d\d\d     Find seven-digit phone number
\b\d{3}-\d{4}         Find seven-digit phone number a better way
^\d{3}-\d{4}$         Validate a seven-digit phone number
\d{3}-\d{2}-\d{4}     Social security number



\ba\w*\b              Find words that start with the letter a
\b\w{6}\b             Find six letter words
\b\w{5,6}\b           Find all five and six letter words



(\d{1,3}\.){3}\d{1,3} A simple IP address finder

For more information about grouping, positive and negative lookarounds, Greedy and Lazy, please please take a look to this great article by Jim Hollenhorst.