大家帮忙看看这个程序怎么写的(已解决)

duziteng

UID: 32269
帖子: 84
积分: 193
在线时间: 9 小时

1^# duziteng 发表于 2008-02-05 18:09

大家帮忙看看这个程序怎么写的(已解决)

#!/usr/bin/perl

use strict;
use warnings;

my $tmp='bf792596 119-118 107-270 bf792560 1';

while($tmp=~/([a-z]{1,2}[0-9]{4,6})/g){
my $tmp2=$1;
$tmp=~s/$tmp2/bf792560--/;

}
print $tmp;

这个程序中总是无法运行，不知道是什么原因，请大家帮忙看看，谢谢拉

March.Liu

UID: 10997
帖子: 173
积分: 397
在线时间: 1 天 17 小时

2^# March.Liu 发表于 2008-02-05 18:48

不是不执行，是死循环了，你看看一个是$1取出来是什么，一个是替换模式是否有问题，手头还有点别的事，没来得及调试。
祝你成功：P

duziteng

UID: 32269
帖子: 84
积分: 193
在线时间: 9 小时

3^# duziteng 发表于 2008-02-05 19:30

$1取出来bf792596
是循环的问题，把while换成if运行2次可以，但是我不知道怎么解决

Lonki

UID: 21498
帖子: 1
积分: 2
在线时间: 10 分钟

4^# Lonki 发表于 2008-02-06 00:17

while 改成 for
$1 改成 $_

churchmice

UID: 31829
帖子: 2
积分: 4
在线时间: 10 分钟

5^# churchmice 发表于 2008-02-06 02:37

土人问一下
直接替换不可以么?
你还是说一下你这个程序的目的吧

[Copy to clipboard] [ - ]

CODE:

#!/usr/bin/perl
use strict;
use warnings;
my $tmp='bf792596 119-118 107-270 bf792560 1';
$tmp =~ s/[a-z]{1,2}[0-9]{4,6}/bf92560--/g;
print "$tmp\n";

估计是我理解错误了

churchmice

UID: 31829
帖子: 2
积分: 4
在线时间: 10 分钟

6^# churchmice 发表于 2008-02-06 03:23

QUOTE:

原帖由 duziteng 于 2008-2-5 18:09 发表
#!/usr/bin/perl

use strict;
use warnings;

my $tmp='bf792596 119-118 107-270 bf792560 1';

while($tmp=~/([a-z]{1,2}[0-9]{4,6})/g){
my $tmp2=$1;
$tmp=~s/$tmp2/bf792560--/;

}
p ...

你错误的原因在于(mastering regex)

QUOTE:

Every string in Perl has associated with it a "current match location" at which the transmission first attempts the match. It's a property of the string, and not associated with any particular regular expression. When a string is created or modified, the "current match location" starts out at the beginning of the string

这段话的意思就是说正则引擎在进行匹配的时候是从一个string的pos处开始的(可以用pos来查看,具体见下面的例子),但是每次string改变的这个string的pos就会被reset到string的开头,也就是为0.
下面的代码可以看出您代码的问题所在

[Copy to clipboard] [ - ]

CODE:

#!/usr/bin/perl
use strict;
use warnings;
my $tmp='bf792596 119-118 107-270 bf792560 1';
print "$tmp\n";
while($tmp=~/(?{print "starting match at $`|$'\n"})([a-z]{1,2}[0-9]{4,6})/g){
printf "The current positon is %d\n",pos($tmp);
sleep 1;
my $tmp2=$1;
$tmp=~s/$tmp2/bf792560--/;
printf "The current positon is %d\n",pos($tmp);
}
print $tmp . "\n";
[/color]
说明一下:
1.
[code]
while($tmp=~/(?{print "starting match at $`|$'\n"})([a-z]{1,2}[0-9]{4,6})/g)

这段代码就是除了匹配以外在每次匹配前打印出匹配的开始出(用|界定),具体看$`,$'什么意思
2.在一次匹配以后打印下string的pos值
然后再修改过$tmp以后再打印下string的pos值

运行结果如下:

QUOTE:

<lig@other-server:~/chinaunix>$ ./test
bf792596                                     119-118       107-270       bf792560       1
starting match at |bf792596                                     119-118       107-270       bf792560       1
The current positon is 8
Use of uninitialized value in printf at ./test line 11.
The current positon is 0
starting match at |bf792560--                                     119-118       107-270       bf792560       1
The current positon is 8
Use of uninitialized value in printf at ./test line 11.
The current positon is 0
starting match at |bf792560----                                     119-118       107-270       bf792560       1
The current positon is 8
Use of uninitialized value in printf at ./test line 11.
The current positon is 0
starting match at |bf792560------                                     119-118       107-270       bf792560       1
The current positon is 8
Use of uninitialized value in printf at ./test line 11.
The current positon is 0
starting match at |bf792560--------                                     119-118       107-270       bf792560       1
The current positon is 8
Use of uninitialized value in printf at ./test line 11.
The current positon is 0
starting match at |bf792560----------                                     119-118       107-270       bf792560       1
The current positon is 8

从这里可以看到
每次匹配都是从string的开头开始的,匹配后string的position设置为8,然后改变了$tmp以后,string的position又reset成0
这样就造成了死循环

如果你一定要用这样的方法
那么可以先把string的pos保留
然后赋值以后再恢复

[Copy to clipboard] [ - ]

CODE:

my $pos = pos($tmp);
my $tmp2=$1;
$tmp=~s/$tmp2/bf792560--/;
pos($tmp) = $pos;

这样可以避免出现死循环
但是是有个小bug的(不能替换第二次出现的bf792560)
问题出在您用的替换上

[Copy to clipboard] [ - ]

CODE:

$tmp=~s/$tmp2/bf792560--/;

可以改成全局替换

[Copy to clipboard] [ - ]

CODE:

$tmp=~s/$tmp2/bf792560--/g;

最后完整的代码(加上一些debug信息)如下

[Copy to clipboard] [ - ]

CODE:

#!/usr/bin/perl
use strict;
use warnings;
my $tmp='bf792596 119-118 107-270 bf792560 1';
print "$tmp\n";
while($tmp=~/(?{print "starting match at $`|$'\n"})([a-z]{1,2}[0-9]{4,6})(?{print "matched at $`<$&>$'\n"})/g){
printf "The current positon is %d\n",pos($tmp);
my $pos = pos($tmp);
my $tmp2=$1;
$tmp=~s/$tmp2/bf792560--/g;
pos($tmp) = $pos;
printf "Restore positon is %d\n",pos($tmp);
}
print $tmp . "\n";

运行结果

QUOTE:

<lig@other-server:~/chinaunix>$ ./test
bf792596 119-118 107-270 bf792560    1
starting match at |bf792596 119-118 107-270 bf792560    1
matched at <bf792596> 119-118 107-270 bf792560    1
The current positon is 8
Restore positon is 8
starting match at bf792560-- 119-118 107-270 |bf792560    1
matched at bf792560-- 119-118 107-270 <bf792560>    1
The current positon is 42
Restore positon is 42
bf792560---- 119-118 107-270 bf792560--    1

duziteng

UID: 32269
帖子: 84
积分: 193
在线时间: 9 小时

7^# duziteng 发表于 2008-02-08 10:40

谢谢大家