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+++ Common patterns 
+++ Common patterns 



**Matching empty** 



What, if you want to match "nothing"? [http://suggestions.yahoo.com/detail/?prop=Pipes&fid=96717 Hapdaniel] has the solution: 



* [^(?!.)] 





**Matching not empty** 



And here's the opposite, again from the suggestion thread. 



* [^(?=.)] 




**Removing whitespace** 
**Removing whitespace** 


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* [()]  groups. You can use the groups matched in the replacement field. For example replace [(\d)] with [0$1] results in a leading zero added. 
* [()]  groups. You can use the groups matched in the replacement field. For example replace [(\d)] with [0$1] results in a leading zero added. 
* [[]]  character groups. For example, [123] matches 1, 2 or 3. 
* [[]]  character groups. For example, [123] matches 1, 2 or 3. 


* [^\d]  combination. ^ means not, \d means digit. So one character, being everything but a digit, is matched here 
* [!\d]  combination. ! means not, \d means digit. So one character, being everything but a digit, is matched here 
* [\d*]  '*' means: 0 to n matches. This would match no or up to infinite digits. 
* [\d*]  '*' means: 0 to n matches. This would match no or up to infinite digits. 
* [\d+]  '+' means: 1 to n matches. At least one. This would match one or more digits. 
* [\d+]  '+' means: 1 to n matches. At least one. This would match one or more digits. 

