• [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
    代码
    @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!

     

     

    - Make people around you successful is the biggest contribution to ourselves. -

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  • 原文地址:https://www.cnblogs.com/zencorn/p/1740064.html
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