grep返回一个数字中符合条件的所有元素；map对数字中所有元素实施转化并返回结果。两者都遍历了数组，但一个用来搜索，一个用来转化。两者都支持表达式或者代码块。
#!/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"; 参考：http://mailman.linuxchix.org/pipermail/courses/2003-November/001368.html