Perl file operation

Open function

The following code we use open the function opens the file as read-only (<) file.txt :

open(DATA, "<file.txt");

< represents read-only mode.

In the code DATA for the file handle to read the file, the following example opens the file and outputs the contents of the file:

#!/usr/bin/perlopen(DATA,"<file.txt")ordie"file.txt
File cannot be opened,$!";while(<DATA>){print"$\_";}

open(DATA, ">file.txt") or die "file.txt File cannot be opened, $!";

open(DATA, "+<file.txt"); or die "file.txt File cannot be opened, $!";

open DATA, "+>file.txt" or die "file.txt File cannot be opened, $!";

open(DATA,">>file.txt") || die "file.txt File cannot be opened, $!";

open(DATA,"+>>file.txt") || die "file.txt File cannot be opened, $!";

Sysopen function

sysopen function is similar to open functions, but their arguments are not the same.

The following example opens the file with read-write (+ < filename):

sysopen(DATA, "file.txt", O_RDWR);

If you need to empty the file before updating it, write as follows:

sysopen(DATA, "file.txt", O_RDWR|O_TRUNC );

You can use O_CREAT to create a new file O_WRONLY for write-only mode O_RDONLY in read-only mode.

The PERMS parameter is an octal attribute value, which represents the permissions after the file is created. The default is 0x666 .

The following table lists the possible pattern values:

Close function

After the file is used, to close the file to flush the input and output buffer associated with the file handle, the syntax for closing the file is as follows:

close FILEHANDLE
close

FILEHANDLE is the specified file handle, and returns if closed successfully true .

close(DATA) || die "cannot close file";

Read and write files

There are several different ways to read and write information to a file:

< FILEHANDL > operator

The main way to read information from an open file handle is <FILEHANDLE> operator. In a scalar context, it returns a single line from the file handle. For example:

#!/usr/bin/perlprint"Novice Tutorial website?\\n";$name=
<STDIN>;print"website：$name\\n";

$ cat import.txt
1
2
3

#!/usr/bin/perlopen(DATA,"<import.txt")ordie"Unable to open data";@lines=
<DATA>;print@lines;# Output array contentclose(DATA);

1
2
3

Getc function

xgetc function from the specified FILEHANDLE returns a single character, if it is not specified STDIN :

getc FILEHANDLE
getc

If an error occurs, or if the file handle is at the end of the file, return``undef`` .

Read function

read function is used to read information from the file handle of the buffer.

This function is used to read binary data from files.

read FILEHANDLE, SCALAR, LENGTH, OFFSET
read FILEHANDLE, SCALAR, LENGTH

Parameter description:

• FILEHANDLE :A file handle that holds a unique identifier of a file

• SCALAR : store the results, if not specified OFFSET the data will be placed in the beginning of SCALAR . Otherwise, the data is placed inthe SCALAR in OFFSET after the byte.

• LENGTH :The length of the content read

• OFFSET : offset.

If the read is successful, the number of bytes read is returned, if 0 is returned at the end of the file, and if an error occurs undef .

Print function

For all functions that read information from a file handle, the main write function at the back end is print :

print FILEHANDLE LIST
print LIST
print

Using file handles and print function can send the result of the program to the output device (STDOUT: standard output), for example:

print "Hello World!\n";

File copy

For the following example, we will open an existing file file1.txt and read every line of it written to the file file2.txt :

#!/usr/bin/perl# Open file in read-only mode open(DATA1,"<file1.txt");#
Open a new file and write to it open(DATA2,">file2.txt");#
Copy Data while(<DATA1>){printDATA2$\_;}close(DATA1);close(DATA2);

File renaming

For the following example, we will have an existing file file1.txt rename to file2.txt , the specified directory is in the /usr/runoob/test/ below:

#!/usr/bin/perl

rename ("/usr/runoob/test/file1.txt", "/usr/runoob/test/file2.txt" );

Function renames only two parameters are accepted and only existing files are renamed.

Delete a file

The following example shows how to use the unlink function to delete the file:

#!/usr/bin/perlunlink("/usr/runoob/test/file1.txt");

Specify the file location

You can use it. tell function to get the location of the file and by using the seek function to specify the location within the file:

Tell function

tell function is used to get the file location:

tell FILEHANDLE
tell

If you specify FILEHANDLE this function returns the position of the file pointer, in bytes. If not specified, the default selected file handle is returned.

Seek function

seek() function reads or writes a file by moving the file read-write pointer through the file handle, reading and writing in bytes:

seek FILEHANDLE, POSITION, WHENCE

Parameter description:

• FILEHANDLE :A file handle that holds a unique identifier of a file

• POSITION :Represents the number of bytes to be moved by the file handle (read-write position pointer)

• WHENCE :Represents the starting position of the file handle (read-write position pointer) when it starts to move. The values you can take are 0, 1, and 2; they represent the beginning of the file, the current location, and the end of the file, respectively.

The following example reads 256 bytes from the beginning of the file:

seek DATA, 256, 0;

File information

The Perl file operation can also test whether the file exists, whether it can be read or written, and so on.

We can first create file1.txt document is as follows:

$ cat file1.txt
www.runoob.com

#/usr/bin/perlmy$file="/usr/test/runoob/file1.txt";my(@description,$size);if(-e$file){push@description,
'it is a binary file'if(-B\_);push@description,'it is a socket (socket)'if(-S\_);push@description,
'it is a text file'if(-T\_);push@description,'it is a special block file'if(-b\_);push@description,
'it is a special character file'if(-c\_);push@description,'it is a directory'if(-d\_);push@description,
'file exists'if(-x\_);push@description,(($size=
-s\_))?"$size byte":'blank';print"$file information：",join(',',@description),"\\n";}

file1.txt information: It is a text file with 15 bytes