第七章 正则模式

模式分组:在数学中,圆括号() 用来分组。因此,圆括号也是元字符模式/fred+/ 会匹配像fredddddd这样的字符窜/(fred)+/ 会匹配像fredfredfred这种字符窜[root@jhoa 2015]# cat a8.pl $_="abba";if (/(.)\1/){ ##匹配bb print "It matched same character next to itself!\n"; print "\$1 is $1\n";}[root@jhoa 2015]# perl a8.pl It matched same character next to itself!$1 is b(.)\1 表明需要匹配连续出现的两个同样的字符反向引用不必总是附在相应的括号后面,下面的模式会匹配y后面的4个连续的非回车字符,并且用\1在d字符之后重复这个4个字符[root@jhoa 2015]# cat a9.pl $_ = "yabba dabba doo";if (/y(....) d\1/) {  print "It matched the same after y and d !\n";  print "\$1 is $1\n";}[root@jhoa 2015]# perl a9.pl It matched the same after y and d !$1 is abba[root@jhoa 2015]# cat a11.pl $_ = "yabba dabba doo";if (/y(.)(.)\2\1/)  {  print "It matched the same after y and d !\n";  print "\$1 is $1\n";  print "\$2 is $2\n";}[root@jhoa 2015]# perl a11.pl It matched the same after y and d !$1 is a$2 is b匹配的是abba$_ = "yabba dabba doo";if (/y((.)(.)\3\2) d\1/) {  print "It matched the same after y and d !\n";  print "\$1 is $1\n";  print "\$2 is $2\n";}~                                                                                                    ~  (/y((.)(.)\3\2) d\1/)                                                                                                   ~    [root@jhoa 2015]# cat a10.pl $_ = "yabba dabba doo";if (/y((.)(.)\3\2) d\1/) {  print "It matched the same after y and d !\n";  print "\$1 is $1\n";  print "\$2 is $2\n";  print "\$3 is $3\n";}[root@jhoa 2015]# perl a10.pl It matched the same after y and d !$1 is abba$2 is a$3 is b匹配abbd dabbd d