perl 学习 --2013-4-11

内容：

1.q,qq,qw,qx

2.$_

3.打开文件2种方式

4.defined,undef

执行（1）

[root@zbk11g ~]# perl -e'
> print q/this is a bike\n/;
> '
this is a bike\n[root@zbk11g ~]#

[root@zbk11g ~]# perl -e'
> print qq/this is a bike\n/;
> '
this is a bike

[root@zbk11g ~]# perl -e'
> print qw/this is a bike\n/;
> '
thisisabike\n[root@zbk11g ~]#

[root@zbk11g ~]# perl -e'
> print qx/this is a bike\n/;
> '
[root@zbk11g ~]# perl -e'
> print qx/date/;
> '
Wed Apr 10 19:16:19 PDT 2013
[root@zbk11g ~]#

小结：q=单引，qq=双引，qw={'$name1','$name2'},qx=反引··，并且qw在输出时只输出变量不包含空格；

（2）

$_为默认输入变量

[root@zbk11g ~]# perl p9
china is my motherland
do|you|know
[root@zbk11g ~]# more p9
#!/usr/bin/perl
open("FL2","txt") or die "can't open the file!";
while(<FL2>)
{
print $_; #文本的第一行，第二行循环输出；
}
close FL2;
[root@zbk11g ~]# more txt
china is my motherland
do|you|know

（3）

1.

[root@zbk11g ~]# more p9
#!/usr/bin/perl
open("FL2","txt") or die "can't open the file!";
while(<FL2>)
{
print $_;
}
close FL2;

2.

[root@zbk11g ~]# more p9
#!/usr/bin/perl
#open("FL2","txt") or die "can't open the file!";
open "FL2","<","txt" or die "can't open the file!";
while(<FL2>)
{
print $_;
}
close FL2;

(4)

[root@zbk11g ~]# perl p9
OK
[root@zbk11g ~]# more p9
#!/usr/bin/perl
$na="name";
print "OK\n" if defined $na;

[root@zbk11g ~]# perl p9
[root@zbk11g ~]# more p9
#!/usr/bin/perl
$na="name";
undef $na;
print "OK\n" if defined $na;

小结：defined判断后面的变量是否有效，有效有1，无效为0；undef将原定义的变量失效；