[转 改] Perl初级教程 （三）

【文件处理】

下面是一个简单的perl程序，与UNIX中cat命令对某个文件的操作相同。

#!/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 file
open(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操作。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 array
close(INFO);			# Close the file
print @lines;			# Print the array

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#open语句也可以对文件进行输出和附加操作。可以在文件名前加>进行输出操作，用>>进行附加操作：
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

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

 每次的操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("Hello World!");
}
> 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 = "A";
$StrB = "0";

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