Perl学习笔记(4)文件的输出输入

1. 文件名前面没有">"表示读文件
open(FILE,"C:\test.txt");
while(<FILE>)
{
        chomp;
        print "$_\n";
}
close(FILE);


2. 文件名前面有一个">"表示写文件，并覆盖原有内容
open(FILE,">C:\test.txt");
print FILE "大家好\n";
close(FILE);


3. 文件名前面有两个">"表示在这个文件后面追加内容
open(FILE,">>C:\test.txt");
print FILE "大家好\n";
close(FILE);


4. 一次性将文件中的所有内容读入一个数组中(该方法适合小文件)：


open(FILE,"filename")||die"can not open the file: $!";
@filelist=<FILE>;


foreach $eachline (@filelist) {
        chomp $eachline;
}
close FILE;


@filelist=<FILE>;
当文件很大时，可能会出现"out of memory"错误，这是可以采用如下方法，一次读取一行。


5. 一次从文件中读取一行，一行行地读取和处理(读取大文件时比较方便)： 


open(FILE,"filename")||die"can not open the file: $!";


while (defined ($eachline =<FILE>)) {
     chomp $eachline;
         # do what u want here!
}
close FILE;


6. STDIN, STDOUT, STDERR and DATA - Perl file handles
STDIN - Standard Input, for user control input, typically the keyboard
STDOUT - Standard Output,for regular use output, typically the screen
STDERR - Standard Error, for error output; typically defaults to the screen too
  例print STDERR "this is an apple."; 
DATA - Input for data stored after __END__ at the end of the program