Perl中的grep和map

grep返回一個數字中符合條件的所有元素；map對數字中所有元素實施轉化並返回結果。兩者都遍歷了數組，但一個用來搜索，一個用來轉化。兩者都支持表達式或者代碼塊。

#!/usr/bin/perl -w
use strict;

#get positive number
my @number = (1,2,3, -1,-5);
my @positive_number = grep  $_ > 0, @number;
print "\@number: (@number)\n";
print "\@positive_number: (@positive_number)\n";

#get sqrt
my @sqrt_number  = map sqrt $_, @positive_number;
print "\@sqrt_number: (@sqrt_number)\n";

#split words
my @lines = ( "hello world", "not too bad" );
my @words = map m/\b(\w+)\b/g, @lines;
print "\@lines size: " . @lines . " (@lines)\n";
print "\@words size: " . @words . " (@words)\n";

#modify email address
my @email_addresses = ( "fei\@gmail.com", "fei\@sina.com.cn" );
my @disguised_addresses = map {
	my $email = $_;
	$email =~ s/\@/ at /;
	$email =~ s/\./ dot /g;
	$email;
} @email_addresses;
print "\@email_addresses: (@email_addresses)\n";
print "\@disguised_addresses: (@disguised_addresses)\n";

參考：http://mailman.linuxchix.org/pipermail/courses/2003-November/001368.html