[转 - 改] Perl初级教程 （三）

概述【文件处理】 下面是一个简单的perl程序，与UNIX中cat命令对某个文件的 *** 作相同。 #!/usr/local/bin/perl## Program to open the password file, read it in,# print it, and close it again. $file = '/export/home/dwei/ProgramScriptFol

【文件处理】

下面是一个简单的perl程序，与UNIX中cat命令对某个文件的 *** 作相同。

#!/usr/local/bin/perl## Program to open the password file,read it in,# print it,and close it again.
$file = '/export/home/DWei/ProgramScriptFolder/Textfile';	# name the fileopen(INFO,$file);		# Open the file

#open(INFO,'/export/home/DWei/ProgramScriptFolder/Textfile'); # open函数打开一个文件并进行读 *** 作。第一个参数filehandle是指向文件的句柄。第二个参数为被打开的文件的文件名

@lines = <INFO>;		# Read it into an arrayclose(INFO);			# Close the fileprint @lines;			# Print the array

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#open语句也可以对文件进行输出和附加 *** 作。可以在文件名前加>进行输出 *** 作，用>>进行附加 *** 作：
 
 
open(INFO,">$file"); # Open for output 
> [返回空，文件内容也清空]
 

open(INFO,">>$file");  　　　　 # Open for appending
print INFO "Hello World!";　　  # input the text to file.　
close(INFO);
open(INfile,"$file");
@lines = <INfile>;
close(INfile);
print @lines;
 
> Hello World ! Hello World ! 
 

 

 【控制结构】

foreach

      
代码                  @FruitList           =      (     @H_419_114@"     @H_419_114@Apple      @H_419_114@"     ,     @H_419_114@"     @H_419_114@Pear      @H_419_114@"     ,     @H_419_114@"     @H_419_114@Orange      @H_419_114@"     ,     @H_419_114@"     @H_419_114@Peach      @H_419_114@"     );
     print     (     @H_419_114@"     @H_419_114@\n     @H_419_114@"     );
     print     (     @FruitList     );
     print     (     @H_419_114@"     @H_419_114@\n     @H_419_114@"     );
     foreach           $Item      (     @FruitList     )
{
         print     (     @H_419_114@"     @H_419_114@\n     @H_419_114@"     );
         print     (     $Item     );
}
     >      Apple
  Pear
  Orange
  Peach                                     
 for
 

 每次的 *** 作过程被包围在花括号内。程序块中的$Item第一次被赋予@FruitList数组中的第一个值，然后被赋予数组的第二个值，依次类推。如果@FruitList是空的，那么程序块将不会被执行

 

【判断】

判断是检验表达式结果是真是假的一种结构。在Perl中，任何非0数字和非空字符串被看作真。数字0、0字符串和空字符串被看作假。下面是一些基于数字和字符串的判断

 

$NumberA   =   1 ;
$NUmberB   =   2 ;
if  ( $NumberA   !=   $NumberB )  # == Is $a numerically equal to $b? {
     print ( @H_419_114@" @H_419_114@Hello World! @H_419_114@" );
}
>  Hello World !  

$StrA = "A";
$StrB = "B";

if ($StrA eq $StrB)     # eq :Is $a string-equal to $b?
{
 print("Hello World!");
}　　　　　　　　　　　　　　# ne : Is $a string-equal to $b?
else
{
 print("Here!");
}

> Here!  

 

 【逻辑】

 

$StrA   =   @H_419_114@" @H_419_114@A @H_419_114@" ;
$StrB   =   @H_419_114@" @H_419_114@0 @H_419_114@" ;

if  ( $StrA   &&   $StrB )
{
     print ( @H_419_114@" @H_419_114@Hello World! @H_419_114@" );
}
else
{
     print ( @H_419_114@" @H_419_114@Here! @H_419_114@" );
}
  >  Here !  

$StrA = "A";
$StrB = "0";

if ($StrA || $StrB)
{
 print("Hello World!");
}
else
{
 print("Here!");
}

 > Hello World!  

$StrA = "A";
$StrB = "0";

if (! $StrB)
{
 print("Hello World!");
}
else
{
 print("Here!");
}

> Hello World!

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