[问题]一个关于perl 的正则表达式的问题

[banban]

突然想起来，perl里面有个叫\G（具体需要查书……）的标签，是从上次匹配结束开始匹配。
用这个就可以了

有\G吗？我只记得有一个/g是用于全局替换的，等等我查一下阿……

[wuchuanren]

原来楼主还在关心，那我贴一段代码吧 :

代码： 全选

#!/usr/bin/perl -w
$data="atggcagttggtacctaagcattdggtacccgtta";
while($data =~ /\G.*?(.{4}ggtacc)/g){
        print $1,"\n";
}
~

呵呵，只是有个小地方不知道是否符合楼主的要求

[wuchuanren]

像这样做有个特点:
比如这么一串碱基

代码： 全选

atggcagttggtaccttdggtacccgtta

前后有两个ggtacc,后面一个ggtacc结尾的长度为10的串的前半部分含有上一个ggtacc的一部分内容，这段代码就不能完美解决

所以具体采用什么方法需要看楼主的需求:em01




(最近复习回一点perl啦～～)

[banban]

哦，这样的运行结果也是正确的。多谢你提供的另一种方法。
可是关于这个 \G ，我还是不知道它是如何用的，课本上没有讲到，也google 不到。不过，还是多谢了，呵呵。

[wuchuanren]

\G和 \b一样只是一个锚点，指示上次匹配结束的位置（如果没有匹配或者匹配失败就回到字符串的起点）。
\G在/g的时候有效。
使用\G的时候有个/c修饰符，用了/c修饰符，匹配失败了不回到起点。
................

[banban]

恩，原来如此，多谢了，亏我还学了几个月的perl 呢，好多东西都还没掌握，呵呵，见笑了……

[heejun]

哦，这样的运行结果也是正确的。多谢你提供的另一种方法。
可是关于这个 \G ，我还是不知道它是如何用的，课本上没有讲到，也google 不到。不过，还是多谢了，呵呵。

有兴趣的话可以看mastering regular expression
里面很详细的

\G was first introduced by Perl to be useful when doing iterative matching with /g (☞51), and ostensibly matches the location where the previous match left off. On the first iteration, \G matches only at the beginning of the string, just like \A.
If a match is not successful, the location at which \G matches is reset back to the beginning of the string. Thus, when a regex is applied repeatedly, as with Perl's s/⋯/⋯/g or other language's "match all" function, the failure that causes the "match all" to fail also resets the location for \G for the next time a match of some sort is applied.

Type of match Where match starts pos upon success pos upon failure
m/⋯/ start of string (pos ignored) reset to undef reset to undef
m/⋯/g starts at target's pos set to end of match reset to undef
m/⋯/gc starts at target's pos set to end of match left unchanged

[banban]

哦，这样的运行结果也是正确的。多谢你提供的另一种方法。
可是关于这个 \G ，我还是不知道它是如何用的，课本上没有讲到，也google 不到。不过，还是多谢了，呵呵。

有兴趣的话可以看mastering regular expression
里面很详细的

\G was first introduced by Perl to be useful when doing iterative matching with /g (☞51), and ostensibly matches the location where the previous match left off. On the first iteration, \G matches only at the beginning of the string, just like \A.
If a match is not successful, the location at which \G matches is reset back to the beginning of the string. Thus, when a regex is applied repeatedly, as with Perl's s/⋯/⋯/g or other language's "match all" function, the failure that causes the "match all" to fail also resets the location for \G for the next time a match of some sort is applied.

Type of match Where match starts pos upon success pos upon failure
m/⋯/ start of string (pos ignored) reset to undef reset to undef
m/⋯/g starts at target's pos set to end of match reset to undef
m/⋯/gc starts at target's pos set to end of match left unchanged

多谢了哦……又有新的收获了，呵呵