Perl学习笔记(5)glob的使用

######################read()函数中的offset参数含义
read (FILEHANBD, $var, $length, $offset)
read 函数有四个参数，最容易误解的是$offset
它的含义看官方文档，解释是:

An OFFSET may be specified to place the read data at some place in the string other than the beginning. A negative OFFSET specifies placement at that many characters counting backwards from the end of the string. A positive OFFSET greater than the length of SCALAR results in the string being padded to the required size with "\0" bytes before the result of the read is appended.

#####################优化技巧

函数的开销是很大的。
A循环地调用一个函数
B在函数中循环地进行一个操作
从性能上说，B比A好。


#####################glob的用法--读取一个目录下的所有文件
1. 比如要读取/home/globtest目录中的所有文件，可以这样写：@plFiles = glob '/home/globtest/*.*';
上面的glob的用法相当于如下
opendir(Dir,"/home/globtest");#注意这是在Linux的写法，若在Windows下，应该写为opendir(Dir,"F:\\home\\globtest");
@Files=readdir(Dir);
closedir(Dir);
foreach $Cur(@Files){
$File="/home/globtest".$Cur;
open(IN,$File);
while(<IN>){
......
                   }
close(IN);
}


2 . @many = glob "{apple,tomato,cherry}={green,yellow,red}";
把@many数组输出就能看到会显示:
1 apple=green
2 apple=yellow
3 apple=red
4 tomato=green
5 tomato=yellow
6 tomato=red
7 cherry=green
8 cherry=yellow
9 cherry=red