perl - 基础

第二章 标量数据

    #!/usr/bin/perl -w
    $pi = 3.141592654;
    $circ = 2 * $pi * 12.5;
    print "The circumference of a circle of radius 12.5 is $circ.\n";

 print "Enter first number: ";
    chomp($one = <STDIN>);
    print "Enter second number: ";
    chomp($two = <STDIN>);
    $result = $one * $two;
    print "The result is $result.\n";

 print "Enter a string: ";
    $str = <STDIN>;
    print "Enter a number of times: ";
    chomp($num = <STDIN>);
    $result = $str x $num;
    print "The result is:\n$result";

第三章 列表和数组

print "Enter some lines, then press Ctrl-D:\n"; # or maybe Ctrl-Z
    @lines = <STDIN>;
    @reverse_lines = reverse @lines;
    print @reverse_lines;

   @names = qw/ fred betty barney dino wilma pebbles bamm-bamm /;
    print "Enter some numbers from 1 to 7, one per line, then press Ctrl-D:\n";
    chomp(@numbers = <STDIN>);
    foreach (@numbers) {
      print "$names[ $_ - 1 ]\n";
    }

print sort <STDIN>;

第四章 子程序

sub marine {
$n += 1; #全局变量$n
print "Hello, sailor number $n!\n";
}

&marine; #输出Hello, sailor number 1!
&marine; #输出Hello, sailor number 2!
&marine; #输出Hello, sailor number 3!
&marine; #输出Hello, sailor number 4!

$n = &max(44,15,22);
print "$n";

sub max{
	if(@_!=2){
print "WARNING! &max should get exactly two arguments!\n";
return;
}

	if($_[0] > $_[1]){
		print "$_[0]\n";
	}else{
		print "$_[1]\n";
	}
	return $_[0] + $_[1];
}

    sub total {
      my $sum;  # private variable
      foreach (@_) {
        $sum += $_;
      }
      return $sum;
    }

my @fred = qw{ 1 3 5 7 9 };
my $fred_total = &total(@fred);
print "The total of \@fred is $fred_total.\n";
print "The numbers from 1 to 1000 add up to ", &total(1..1000), ".\n";

写一个子程序，名为&above_average，将一列数字作为其参数，返回所有大于平均值的数字

sub total {
  my $sum;  # private variable
  foreach (@_) {
    $sum += $_;
  }
  $sum;
}

sub average {
  if (@_ == 0) { return }
  my $count = @_;
  my $sum = &total(@_);               # from earlier exercise
  $sum/$count;
}
sub above_average {
  my $average = &average(@_);
  my @list;
  foreach $element (@_) {
    if ($element > $average) {
      push @list, $element;
    }
  }
  @list;
}

my @fred = &above_average(1..10);
print "\@fred is @fred\n";
print "(Should be 6 7 8 9 10)\n";
my @barney = &above_average(100, 1..10);
print "\@barney is @barney\n";
print "(Should be just 100)\n";

第五章 输入与输出

while(<STDIN>){
print "I saw2 $_\n";
}

while(<>){
chomp;
print "It was $_ that I saw!\n";
}

输出到文件

$output = "test.txt";
open FH,">", "$output";
print FH "Tristan Blenheim 101\n";
print FH "Betty Boop 201\n";
print FH "Igor Chevsky 301\n";
print FH "Norma Cord 401\n";
print FH "Jonathan DeLoach 501\n";
print FH "Karen Evich 601\n";
close FH;

文件-> 控制台

open IN, "<", "test.txt" or die;
@a = <IN>;
close IN;
print "@a";

格式化数据

open FH, "<", "test.txt";
foreach $line(<FH>){
	$line =~ s/\x0D?\x0A?$//; #取得一行，去掉结尾换行符
	@datas = split(" ",$line); #把空格当中分隔符，取得数据
	print "@datas\n";
}

输出到错误文件
运行命令chapter5.pl 2> err.txt

print "Hello, World!\nabc"; print STDERR "Hi\n";

第六章 哈希

#my %last_name = qw{
#  fred flintstone
#  barney rubble
#  wilma flintstone
#};
my %last_name;
$last_name{"fred"} = "flintstone";
$last_name{"barney"} = "rubble";
$last_name{"wilma"} = "flintstone";

print "Please enter a first name: ";
chomp(my $name = <STDIN>);
print "That's $name $last_name{$name}.\n";

写一个程序，读入一串单词(一个单词一行)◆，输出每一个单词出现的次数。（提示：如果某个作为数字使用值是
undefined 的，会自动将它转换为0。）如果输入单词为fred, barney, dino, wilma, fred（在不同行中），则输出的fred 将为
３。作为额外的练习，可以将输出的单词按照ASCII 排序。

my(@words, %count, $word);     # (optionally) declare our variables
chomp(@words = <STDIN>);
foreach $word (@words) {
  $count{$word} += 1;          # or $count{$word} = $count{$word} + 1;
}
foreach $word (keys %count) {  # or sort keys %count
  print "$word was seen $count{$word} times.\n";
}

exists 函数

my %last_name;
$last_name{"fred"} = "flintstone";
$last_name{"barney"} = "rubble";
$last_name{"wilma"} = "flintstone";

my $name = <STDIN>; #读入下一行；
chomp($name);
if(exists $last_name{$name}){
print "Exists";
}else{
 print "not exists";	
}

第十一章 文件检验

if(-e "test.txt"){
	print "e";
}

第十二章 目录操作
列出某个文件夹下的文件

print "Which directory? (Default is your home directory) ";
chomp(my $dir = <STDIN>);
if ($dir =~ /^\s*$/) {         # A blank line
  chdir or die "Can't chdir to your home directory: $!";
} else {
  chdir $dir or die "Can't chdir to '$dir': $!";
}
my @files = <*>;
foreach (@files) {
  print "$_\n";
}

删除文件

foreach (@ARGV) {
      unlink $_ or warn "Can't unlink '$_': $!, continuing...\n";
    }

移动文件

    use File::Basename;
    use File::Spec;
    my($source, $dest) = @ARGV;
    if (-d $dest) {
      my $basename = basename $source;
      $dest = File::Spec->catfile($dest, $basename);
    }
    rename $source, $dest
      or die "Can't rename '$source' to '$dest': $!\n";

第十一章 字符串和排序
数字排序

my @numbers;
while (<>) {
  push @numbers, split;
}

foreach (sort { $a <=> $b } @numbers) {
  printf "%20g\n", $_;
}

字母排序

my @letters;
while (<>) {
  push @letters, split;
}

foreach (sort { $a cmp $b } @letters) {
  printf  "$_\n";
}

第十四章 进程管理
调用系统命令

 chdir "c:/" or die "Can't chdir to root directory: $!";
    exec "dir" or die "Can't exec dir: $!";