1. $&, $`,$' 用在模式匹配中

$&  用来存放匹配中的值
$`   用来存放匹配中之前所有字符
'   用来存放匹配中之后所有字符

#!/usr/bin/perl -w
if("Hello good  there,neigbor hello" =~ /S(w+),/)
print "That actually matched '$&'. ";
print $`." ";
print $'." ";


That actually matched 
Hello good  
neigbor hello




2. Perl - $_ and @_

Perl's a great language for special variables - variables that are set up without the programmer having to intervene and providing information ranging from the number of lines read from the current input file ($.) through the current process ID ($$) and the operating system ($^O). Other special variables effect how certain operations are performed ($| controlling output buffering / flushing, for example), or are fundamental in the operation of certain facilities - no more so than $_ and @_.

Lets clear a misconception. $_ and @_ are different variables. In Perl, you can have a list and a scalar of the same name, and they refer to unrelated pieces of memory.

$_ is known as the "default input and pattern matching space". In other words, if you read in from a file handle at the top of a while loop, or run a foreach loop and don't name a loop variable, $_ is set up for you. Then any regular expression matches, chops (and lcs and many more) without a parameter, and even prints assume you want to work on $_. Thus:
while ($line = <FH>) {
  if ($line =~ /Perl/) {
    print FHO $line;
  print uc $line;

Shortens to:
while (<FH>) {
  /Perl/ and
    print FHO ;
  print uc;

@_ is the list of incoming parameters to a sub. So if you write a sub, you refer to the first parameter in it as $_[0], the second parameter as $_[1] and so on. And you can refer to$_# as the index number of the last parameter:
sub demo {
  print "Called with ",$#_+1," params/n";
  print "First param was $_[0]/n";

Note that the English module adds in the ability to refer to the special variables by other longer, but easier to remember, names such as @ARG for @_ and $PID for $$. But use English; can have a detrimental performance effect if you're matching regular expressions against long incoming strings.