第一章输入和输出基础

[root@dwh1 perl]# cat 1.pl
#!/usr/bin/perl
#file:lgetl.pl

##装入模块,我们通过use()使用IO::File模块,该模块包含Perl文件操作的面向对象接口

use IO::File;

#处理命令行参数我们通过shift()从命令行中取出文件名并将其存储在名为$file的变量中

my $file = shift;

##我们调用IO::File ->new()方法来打开文件,返回一个文件句柄,存储在$fh中。

##如果你不熟悉面向对象的语法也不要着急
my $fh = IO::File->new($file);

my $line = <$fh>;

print $line;

[root@dwh1 perl]# cat 2.pl
$input = <STDIN>;
chomp ($input);
print STDOUT "$input ";

1.3.2 输入和输出操作:

如何从文件句柄中读取数据,Perl给出了两种选择:一种是一次读取一行,适用于文本文件。

另一种是读取任意长度的数据块,适用于图像文件的2进制字节流

use Errno qw (EACCES ENOENT);
my $result = open (FH,"</var/log/messages");
if (!$result){#oops,something went wrong
print "$! is $! ";
if ($! == EACCESS) {
warn "You do not have permission to open this file.";
}elsif ($! == ENOENT) {
warn "File or directory not found.";
}else {
warn "Some other error occurred:$!"
}
}

1.4.1 对象和引用:

在Perl中,引用(reference)是指向数据结构的指针。你可以使用反斜杠运算符来创建已存在的数据结构的引用。例如:

[oracle@dwh1 perl]$ cat 2.pl
$a = 'hi there';
$a_ref = $a; ##reference to a scalar

print "$a_ref is $$a_ref ";

@b = ('this','is','an','array');

$b_ref = @b; #reference to an array

print "$b_ref is @$b_ref ";

%c = (first_name =>'Fred',last_name => 'Jones');

$c_ref = \%c; ###reference to a hash

print %$c_ref;
print " ";

##-------------------------------------------------------
$a = $b_ref->[2]; ##yields "an"

$b = $c_ref->{last_name}; ##yields "Jones"

print "$a is $a ";

print "$b is $b ";

[oracle@dwh1 perl]$ perl 2.pl
$a_ref is SCALAR(0x2019560)
$a_ref is hi there
$b_ref is this is an array
last_nameJonesfirst_nameFred
$a is an
$b is Jones

如果你打印一个引用,你将获得一个类似SCALAR(0x2019560)的字符窜,该字符串指示引用的类型

和该引用在内存中的位置(没什么用处).

对象(object)也是一个引用,只不过具有一些额外的位,对象带有"是什么模块创建它"的相关信息,它以这种方式被"神圣化"(blessed)而

居于特定模块的软件包中。这些"神圣的"引用将继续和其他引用一样工作。例如,如果一个名为$object的对象时一个神圣化的

散列数组引用,你可按如下所示索引它:

#!/usr/bin/perl
#
use strict;

##装入IO::File模块
use IO::File;

##从命令行中取到要执行行计数的文件的名字并将$counter 变量初始化为0
my $file = shift;

my $counter = 0;
my $fh = IO::File->new ($file) or die;

####$fh 是对象的引用
print "$fh is $fh ";
while (defined (my $line = $fh->getline)){
$counter++;
}
STDOUT->print("Counted $counter lines ")

H:20150226Socket>perl 1.pl 1.txt
$fh is IO::File=GLOB(0x202e0bc)
Counted 202 lines

open (FH,"<1.txt") or die;
$line = <FH>;
print "$line is $line ";
close (FH);

open (FH,"<1.txt") or die;
@lines = <FH>;
print "@lines is @lines ";
close (FH);

$a = <>;
print "$a is $a ";

@a = <>;
print "@a is @a ";

[oracle@dwh1 perl]$ cat a5.pl
open (FH,"<1.txt") or die;
while (<FH>) {
print "Found $_ ";
}
[oracle@dwh1 perl]$ perl a5.pl
Found 11111111

Found 22222222

Found 33333333

<FILEHANDLE> 形式显示地给出读取数据的文件句柄。

$bytes = read(FILEHANDLE,$buffer,$length [,$offset])

$bytes = sysread(FILEHANDLE,$buffer,$length [,$offset])

第一章 输入和输出基础

第一章输入和输出基础