Perl文件读写

Perl File Handling: open, read, write and close files

#====================

Opening files

Solution 1:

Opening a file in perl

open FILE, "filename.txt" or die $!; # read


open FILEHANDLE, MODE, EXPR

The available modes are the following:

mode	operand	create	truncate
read	<
write	>	✓	✓
append	>>	✓

Each of the above modes can also be prefixed with the + character to allow for simultaneous reading and writing.

mode	operand	create	truncate
read/write	+<
read/write	+>	✓	✓
read/append	+>>	✓

open FILE, ">", "filename.txt" or die $!    #write


open FILE, ">filename.txt" or die $!;   #write


Solution 2:

#!/usr/bin/perl

open(FILE, "<file.txt") or die "Couldn't open file file.txt, $!";

while(<FILE>){
   print "$_";
}

Following is the table which gives possible values of different modes

Entities	Definition
< or r	Read Only Access
> or w	Creates, Writes, and Truncates
>> or a	Writes, Appends, and Creates
+< or r+	Reads and Writes
+> or w+	Reads, Writes, Creates, and Truncates
+>> or a+	Reads, Writes, Appends, and Creates

Solution 3:

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

Following is the table which gives possible values of MODE

Entities	Definition
O_RDWR	Read and Write
O_RDONLY	Read Only
O_WRONLY	Write Only
O_CREAT	Create the file
O_APPEND	Append the file
O_TRUNC	Truncate the file
O_EXCL	Stops if file already exists
O_NONBLOCK	Non-Blocking usability

#====================

Reading files

read a text file line-by-line

my @lines = <FILE>;

while (<FILE>) { print $_; }

while (my $line = <FILE>) { ...}

read a file only a few characters at a time

open FILE, "picture.jpg" or die $!; # read

binmode FILE;

my ($buf, $data, $n);

while (($n = read FILE, $data, 4) != 0)

{ print "$n bytes read\n"; $buf .= $data; }

close(FILE);

#====================

Writing files

open FILE, ">file.txt" or die $!; #write


print FILE $str;

close FILE;

#====================

Closing files

open FILE1, "file.txt" or die $!; # read

open FILE2, "picture.jpg" or die $!; # read

...

close FILE2;

close FILE1;

#====================

REF:

http://www.perlfect.com/articles/perlfile.shtml