小时代5-perl 常量、多维数组及变量的初始化

zhengl

下面我们通过两段代码来了解一下perl中常量，数组，及变量的定义和初始化：
常量及数组的初始化：
#!/usr/bin/perl
use strict;
use warnings;
my $test = "asdf";
print "${test}_test2n";
#constant
use constant {
AAA => "aaa",
BBB=> "bbb",
MIN_TOTAL => 12,
SCORE_PASS => 90,
SCORE_RED => 70,
};
print AAA;
print SCORE_PASS;
#two dimesion arrays
my @steps = (
["aaa", "aaavalue"],
["bbb","bbbvalue"],
["ccc","cccvalue"]
);
print "n";
foreach my $i (0 .. $#steps){
print "$steps[$i][0]:$steps[$i][1]n";
}
变量的定义及初始化：
my $a1;
print "$a1n";
my $a2 = undef;
print "$a2n";
if(!defined($a1)){print "a1 is not definedn";}
if(!$a2){print "a2 is not definedn";}
my $a3='';
if(!$a3){print "a3 is empty stringn";}
在定义变量时一定要初始化，或者在使用时判断是否defined，很多的时候还需要判断是否为空字符串。 特别是在使用getopt::long或cgi->query获得参数后要检测是否定义，如果么有定义考虑给予默认值。

　　



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