珀尔 |文件处理介绍

在 Perl 中，FileHandle 将名称与外部文件相关联，该文件可以在程序结束或 FileHandle 关闭之前使用。简而言之，FileHandle 就像一个连接，可用于修改外部文件的内容，并为连接（FileHandle）命名，以便更快地访问和简化。 Perl 中的三个基本 FileHandle 是 STDIN、STDOUT 和 STDERR，它们分别代表标准输入、标准输出和标准错误设备。

文件处理通常是通过 open函数完成的。

Syntax: open(FileHandle, Mode, FileName);

Parameters:

• FileHandle- The reference to the file, that can be used within the program or until its closure.
• Mode- Mode in which a file is to be opened.
• FileName- The name of the file to be opened.

此外，Mode 和 FileName 可以组合在一起形成一个打开的表达式。

Syntax: open(FileHandle, Expression);
Parameters:

• FileHandle- The reference to the file, that can be used within the program or until its closure.
• Expression- Mode and FileName clubbed together.

FileHandle 使用 close函数关闭。

Syntax: close(FileHandle);
Parameters:

• FileHandle- The FileHandle to be closed.

使用 FileHandle 读取和写入文件

从 FileHandle 读取可以通过 print函数完成。

Syntax: print();
Parameters:

• FileHandle- FileHandle opened in read mode or a similar mode.

也可以通过 print函数写入文件。

Syntax: print FileHandle String
Parameters:

• FileHandle- FileHandle opened in write mode or a similar mode.
• String- The String to be inserted in the file.

文件处理的不同模式

Mode	Explanation
“<“	Read Only Mode
“>”	Creates file (if necessary), Clears the contents of the File and Writes to it
“>>”	Creates file (if necessary), Appends to the File
“+<“	Reads and Writes but does NOT Create
“+>”	Creates file (if necessary), Clears, Reads and Writes
“+>>”	Creates file (if necessary), Reads and Appends

例子：
考虑一个包含字符串“Welcome to GeeksForGeeks!!!”的文件 Hello.txt最初。

1. 模式 = “<”
   这是只读模式。此模式用于从文件中逐行读取内容。

   #!/usr/bin/perl
     
   # Opening a File in Read-only mode
   open(r, "<", "Hello.txt");
     
   # Printing content of the File
   print();
     
   # Closing the File
   close(r);
   

   输出：
   

2. 模式=“>”
   这是只写模式。在此模式下打开文件后，文件的原始内容将被清除。如果找不到，它会创建一个同名的新文件。

   #!/usr/bin/perl
     
   # Opening File Hello.txt in Read mode
   open(r, "<", "Hello.txt"); 
     
   # Printing the existing content of the file
   print("Existing Content of Hello.txt: " . ); 
     
   # Opening File in Write mode
   open(w, ">", "Hello.txt"); 
     
   # Set r to the beginning of Hello.txt
   seek r, 0, 0; 
     
   print "\nWriting to File...";
     
   # Writing to Hello.txt using print
   print w "Content of this file is changed";
     
   # Closing the FileHandle
   close(w); 
     
   # Set r to the beginning of Hello.txt
   seek r, 0, 0; 
     
   # Print the current contents of Hello.txt
   print("\nUpdated Content of Hello.txt: ".); 
     
   # Close the FileHandle
   close(r); 
   

   输出：
   

3. 模式=”>>”
   这是附加模式。在此模式下打开文件时，文件的原始内容不会被清除。此模式不能用于覆盖，因为字符串始终附加在末尾。如果找不到，它会创建一个同名的新文件。

   #!/usr/bin/perl
     
   # Opening File Hello.txt in Read mode
   open(r, "<", "Hello.txt"); 
     
   # Printing the existing content of the file
   print("Existing Content of Hello.txt: " . ); 
     
   # Opening the File in Append mode
   open(A, ">>", "Hello.txt"); 
     
   # Set r to the beginning of Hello.txt
   seek r, 0, 0; 
     
   print "\nAppending to File...";
     
   # Appending to Hello.txt using print
   print A " Hello Geeks!!!"; 
     
   # close the FileHandle
   close(A); 
     
   # Set r to the beginning of Hello.txt
   seek r, 0, 0; 
     
   # Print the current contents of Hello.txt
   print("\nUpdated Content of Hello.txt: ".);
     
   # Close the FileHandle
   close(r); 
   

   输出：
   

4. 模式 = “+<”
   这是读写模式。这可用于覆盖 File 中的现有字符串。它无法创建新文件。

   #!/usr/bin/perl
     
   # Open Hello.txt in Read-Write Mode
   open(rw, "+<", "Hello.txt"); 
     
   # Print original contents of the File. 
   # rw is set to the end.
   print("Existing Content of Hello.txt: ".); 
     
   # The string is attached at the end 
   # of the original contents of the file.
   print rw "Added using Read-Write Mode."; 
     
   # Set rw to the beginning of the File for reading.
   seek rw, 0, 0; 
     
   # Printing the Updated content of the File
   print("\nUpdated contents of Hello.txt: ".);
     
   # Close the FileHandle
   close(rw); 
   

   输出：
   

5. 模式 = “+>”
   这是读写模式。 “+<”和“+>”的区别在于“+>”可以创建一个新文件，如果没有找到同名的文件，但“+<”不能。

   #!/usr/bin/perl
     
   # Opening File Hello.txt in Read mode
   open(r, "<", "Hello.txt"); 
     
   # Printing the existing content of the file
   print("Existing Content of Hello.txt: " . ); 
     
   # Closing the File
   close(r);
     
   # Open Hello.txt in Read-Write Mode
   open(rw, "+>", "Hello.txt"); 
     
   # Original contents of the File
   # are cleared when the File is opened
   print("\nContents of Hello.txt gets cleared..."); 
     
   # The string is written to the File
   print rw "Hello!!! This is updated file."; 
     
   # Set rw to the beginning of the File for reading.
   seek rw, 0, 0; 
     
   print("\nUpdated Content of Hello.txt: " .);
     
   # Closing the File
   close(rw);
   

   输出：
   

6. 模式 = “+>>”
   这是读取附加模式。这可用于从文件中读取以及追加到文件中。如果未找到，则会创建一个具有相同名称的新文件。

   # Open Hello.txt in Read-Append Mode
   open(ra, "+>>", "Hello.txt"); 
     
   # Set ra to the beginning of the File for reading.
   seek ra, 0, 0; 
     
   # Original content of the File 
   # is NOT cleared when the File is opened
   print("Existing Content of the File: " . );
     
   print "\nAppending to the File....";
     
   # The string is appended to the File
   print ra "Added using Read-Append Mode"; 
     
   # Set ra to the beginning of the File for reading.
   seek ra, 0, 0; 
     
   # Printing the updated content
   print("\nUpdated content of the File: " . );
     
   # Closing the File
   close(rw);
   

   输出：
   

   重定向输出

   
   可以使用 select函数将输出从控制台重定向到文件中。

   Syntax: select FileHandle;
   Parameters:

   • FileHandle – FileHandle of the File to be selected.

   脚步：

   • 打开一个 FileHandle 来写即“>”、“>>”、“+<”、“+>”或“+>>”。
   • 使用选择函数选择 FileHandle。

   现在，使用 print函数打印的任何内容都被重定向到文件。例子：

   # Open a FileHandle in Write Mode.
   open(File, ">", "Hello.txt"); 
     
   # This sets File as the default FileHandle
   select File; 
      
   # Writes to File
   print("This goes to the File."); 
     
   # Writes to File
   print File "\nThis goes to the File too."; 
     
   # This sets STDOUT as default FileHandle
   select STDOUT; 
   print("This goes to the console.");
     
   # Close the FileHandle.
   close(File); 
   

   控制台中的输出：
   Hello.txt 的内容：
   原始文件：
   

   更新后的文件：