Perl 单词边界

单词边界:

匹配单词边界,就是位于单词(w)和非单词字符(W)之间的零宽度的地方。

就是单词前后必须跟非单词字符

[oracle@jhoa big]$ cat 11.pl 
#$var = "The Great Fred";
$var = "Fred erick the Great";
if ($var =~/Fred/){print "$var
"};


[oracle@jhoa big]$ perl 11.pl 
Fred erick the Great

[oracle@jhoa big]$ cat 11.pl 
#$var = "The Great Fred";
$var = "aFred erick the Great";
if ($var =~/Fred/){print "$var
"};
[oracle@jhoa big]$ perl 11.pl 
[oracle@jhoa big]$ 

Fred前面出现单词字符 ,匹配不上

[oracle@jhoa big]$ cat 11.pl 
#$var = "The Great Fred";
$var = "Freda erick the Great";
if ($var =~/Fred/){print "$var
"};
[oracle@jhoa big]$ perl 11.pl 
[oracle@jhoa big]$

Fred后面出现单词字符匹配不上 

[oracle@jhoa big]$ cat 11.pl 
#$var = "The Great Fred";
$var = "!Fred erick the Great";
if ($var =~/Fred/){print "$var
"};
[oracle@jhoa big]$ perl 11.pl 
!Fred erick the Great
[oracle@jhoa big]$

单词前面出现非单词字符,可以匹配

[oracle@jhoa big]$ cat 11.pl 
#$var = "The Great Fred";
$var = "Fred! erick the Great";
if ($var =~/Fred/){print "$var
"};
[oracle@jhoa big]$ perl 11.pl 
Fred! erick the Great
[oracle@jhoa big]$

单词后面出现非单词字符,可以匹配