Perl文件读写

banbanbai

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:

modeoperandcreatetruncate

read
<




write
>
✓
✓


append
>>
✓

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

modeoperandcreatetruncate

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

EntitiesDefinition

< 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

EntitiesDefinition

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