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**Character classes**
alnum	��ĸ��
alpha	��ĸ
ascii	0 - 127��ascii�ַ�
blank	�ո��ˮƽ�Ʊ��
cntrl	��ַ�
digit	ʮ��(same as \d)
graph	��ӡ�ַ�, ��ո�
lower	Сд��ĸ
print	��ӡ�ַ�,��ո�
punct	��ӡ�ַ�, ��ĸ��
space	�հ��ַ� (��\s�ഹֱ�Ʊ��)
upper	��д��ĸ
word	��ַ�(same as \w)
xdigit	ʮ��

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[:word:]��һ�� perl��չ��[:blank:]��һ�� Perl5.8 �� GNU ��չ�� һ�� perl ��չ��ȡ��ͨ��ǰ��һ��^�� 磬 [12[:^digit:]] ƥ��"1", "2" ��κη��ַ�

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