Instance code for initialization of Perl constants, multidimensional arrays and variables


Example 1:

Copy codeThe code is as follows:
use strict;
use warnings;
my $test = “asdf”;
print “${test}_test2\n”;
use constant {
    AAA => “aaa”,
    BBB=> “bbb”,
    MIN_TOTAL => 12,
    SCORE_PASS => 90,
    SCORE_RED => 70,
print AAA;
#two dimesion arrays
my @steps = (
      [“aaa”, “aaavalue”],
print “\n”;
foreach my $i (0 .. $#steps){
  print “$steps[$i][0]:$steps[$i][1]\n”;

Code 2:

Copy codeThe code is as follows:
my $a1;
print “$a1\n”;
my $a2 = undef;
print “$a2\n”;
if(!defined($a1)){print “a1 is not defined\n”;}
if(!$a2){print “a2 is not defined\n”;}
my $a3=”;
if(!$a3){print “a3 is empty string\n”;}

When defining variables, it is necessary to initialize them, or to determine whether they are defined or not when they are used. In many cases, it is necessary to determine whether they are empty strings. Especially when using getopt:: long or CGI – > query to get parameters, it is necessary to check whether the parameters are defined or not, and if no definitions are considered, give default values.

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