Using Predefined Character Sets

To match a predefined character set, select the Pattern match check box. You can then search the text by using these special predefined character sets:

Character set	Characters in set
[[:alnum:]]	ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz 0123456789
[[:alpha:]]	ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz
[[:blank:]]	(The space character and the tab character)
[[:digit:]]	0123456789
[[:graph:]]	ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz 0123456789 !"#$%&'()*+,-./:;<=>?@[]^_`{ }~
[[:lower:]]	Abcdefghijklmnopqrstuvwxyz
[[:print:]]	ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz 0123456789 !"#$%&'()*+,-./:;<=>?@[]^_`{ }~
[[:punct:]]	!"#$%&'()*+,-./:;<=>?@[]^_`{ }~
[[:upper:]]	ABCDEFGHIJKLMNOPQRSTUVWXYZ
[[:xdigit:]]	0123456789ABCDEF abcdef

To search for a string which consists of a letter, followed by some letters or numbers, followed by that same first letter, you would use a back reference, as shown here: ([[:alpha:]])[[:alnum:]]\{1,\}\1.