perl学习（2）文件处理
1、读取某文件，如果该文件不存在，则报错，并提示出错原因open (DB, "/home/ellie/myfile") or die "Can't open file: $!\n";
运行后提示：Can't open file: No such file or director
2、读写文件的方法：
open(FH, "<filename"); # Opens "filename" for reading.读
# The <; symbol is optional.
open(FH, ">filename"); # Opens "filename" for writing.写
# Creates or truncates file.
open(FH, ">>filename"); # Opens "filename" for appending.追加
# Creates or appends to file.
open(FH, "+<filename"); # Opens "filename" for read, then write.写读后写
open(FH, "+>filename"); # Opens "filename" for write, then read.先写后读
close(FH);
3、打开并打印该文件
#!/usr/bin/perl
open(FH, "<d:/readtest.txt") or die "Can't open file: $!\n";
while(<FH>){ print }
4、文件属性
#!/usr/bin/perl
my $file="d:/readtest.txt";
# Is it readble, writeable, and executable?
print "File is readable, writeable, and executable\n" if -r $file and -w _ and -x _;
# When was it last modified?
print "File was last modified ",-M $file, " days ago.\n";
#若为目录则打印
print "File is a directory.\n " if -d $file; # Is it a directory?
由于此文件实际存在，并且是刚建不久，但只是普通的文本文件，因此最后的结果为
File was last modified 0.0239930555555556 days ago.
若代码：print "File is readable, writeable, and executable\n" if -r $file and -w _ and -x _;
改为：print "File is readable, writeable, and executable\n" if -r $file and -w _ ;
最后的结果则为： File is readable, writeable, and executable
File was last modified 0.0251851851851852 days ago.
-w _为-w $file的简写。
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