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

#This is a practice of perl,as which shows with below perl code...codes.

print "Hello,world!\n";

my $animal = "camel\n";
my $answer = 42;

printf $animal;
print "The animal is $animal\n";
print "The square of $answer is ",$answer * $answer,"\n";

print;

my @test = ("t1","t4","t3");
print $test[0],$test[1],$test[$#test],"\n";
print "@test\n";

my @sorted = sort @test;
print "@sorted\n";

my @backwards = reverse @test;
print "@backwards\n";

my %fcolor = (
  apple => "red",banana => "yellow",);

my $apple = $fcolor{"apple"};
print "apple color is $apple. \n";

my @fruits = keys %fcolor;
my @colors = values %fcolor;
print "list fruits: @fruits. \n";
print "list colors: @colors. \n";

my $variables = {
  scalar => {
    desc => "sigle item",sigil => '$',},array => {
    desc => "ordered list of items",sigil => '@',hash => {
    desc => "key/value pairs",sigil => '%',};
print "scalar begin with a $variables->{'scalar'}->{'sigil'}. \n";
print "array begin with a $variables->{'array'}->{'sigil'}. \n";
print "hash begin with a $variables->{'hash'}->{'sigil'}. \n";


my $x = "x";
my $some_condition = 1;
if ($some_condition) {
  my $y = "y";
  print $x;
  print $y;
}
print $x;
#print $y;
print "\n";

print "unless condition.\n" unless(0);

until (1) {
  print "while condition.\n";
};

foreach (@test) {
  print "array element is $_\n";
}

print "array element is $test[$_]\n" foreach 0 .. $#test;

foreach my $key (keys %fcolor) {
  print "The value of $key is $fcolor{$key} \n";
}

my $a = 1;
$a += 1;
print "$a\n";
$a -= 1;
print "$a\n";
$a .= "x";
print "$a\n";

open(my $in,"<","input.txt") or die "can't open input.txt: $!\n";

#my $line = <$in>;
#my @lines = <$in>;
#print "$line";
#print "@lines";

print stderr "stderr test.\n";

while (<$in>) {
  print "$_";
}
print "\n";

close $in or die "$in: $!";

open(my $out,">","output.txt") or die "can not open output.txt. \n";
print $out "hello world!\nWrite this info into output.txt. \n";
close $out or die "$out: $!";

=pod
while(<>) {
    next if /^$/;
    last if (/q/);
  print;
}
=cut

my $email = "hk.mars\@aol.com";

if ($email =~ /([^@]+)@(.+)/) {
  print "username is $1 \n";
  print "hostname is $2 \n";
}

#subroutines
sub loger {
  my $logmessage = shift;

  open my $logfile,">>","my.log" or die "can not open my.log.$!";
  print $logfile $logmessage;
}

loger("hello loger! \n");

sub square {
  my $num = shift;
  my $sq;

  $sq = $num * $num;
  return $sq;
}


my $sq = square(5);
print "the square result of 5 is $sq \n";

#OO Perl

#Using Perl modules

#The end of this practice,let's start to write project...now...

Yeah,perl is so easy as C. I am so expected to start  the web project using perl. I guess only need one week to hack a website done.

Mars