第三章 Typeglob 和符号表

Typeglob 和符号表:

zjzc01:/root/perl# cat t5.pl 
$a=20;
 {
 local  ($a); ##先保存$a原先的值,新值为undef
 my (@b);     ##Lexical变量
 $a = 10;  ##改变$a的新值
@b = ("wallance","grommit");
print $a;   ##打印结果位"10"
print "
";
print "@b";  ##打印结果位"wallace grommit"
print "
";
};

##代码块结束,又回到全局域中,此时只有$a 有效

print $a;    ##打印出"20",原先的值
print "
";

print @b;    ##打印警告信息,因为不存在全局变量@b
print "
";


zjzc01:/root/perl# perl t5.pl 
10
wallance grommit
20

zjzc01:/root/perl# 



zjzc01:/root/perl# cat t6.pl 
open (LOG ,"<","processor.dat");
 while (<LOG>) { 
chomp;
print "$_ is $_
";
};
zjzc01:/root/perl# perl t6.pl 
$_ is id               :42343              ##雇员号
$_ is Name             :E.F.Schumacher
$_ is Office Hours     :Mon 3-4,Wed 9-9
$_ is Courses          :HS201,SS343        ##讲授课程



zjzc01:/root/perl# cat t6.pl 
open (LOG ,"<","processor.dat");
local $/=undef;
chomp;
 while (<LOG>) { 
print "$_ is $_
";
};
zjzc01:/root/perl# perl t6.pl 
$_ is id               :42343              ##雇员号
Name             :E.F.Schumacher
Office Hours     :Mon 3-4,Wed 9-9
Courses          :HS201,SS343        ##讲授课程


变量$/  中保存输入记录分隔符(默认为"
").


砖石操作符使用它来返回下一条记录(默认为下一行).如果你取消该变量值的定义(undef），


整个文件就会被一口气全部读进来。 为了免于保存于恢复$/的原始值,你可以像下面这样使用local操作符:


Typeglob:

我们前面提到typeglob可以被局部化(只能使用local), 还可以相互赋值。通过typeglob 赋值可以创建标示符的别名

例如:

zjzc01:/root/perl# cat t7.pl 
$spud = "Wow!";

@spud = ("idaho","result");

*potato = *spud;

print "$potato is $potato
";
print "@potato is @potato
";

zjzc01:/root/perl# perl t7.pl 
$potato is Wow!
@potato is idaho result



$!  返回值:

app01:/home/tomcat> cat 1.pl 
unlink{'/root/1.sh'};

if ($!){print "$!","
"};
app01:/home/tomcat> perl 1.pl 
No such file or directory