thanks everybody who give me advice.

To BrowserUk ,I don't understand how to get interpolated as string when it is "^0\$".Can you explain more detail? thanks!

The reason for the observed behaviour is that a regex with "s as the delimiter get interpolated as a string, before it gets treated as a regex.

my test script like this:

$_ = '0$';
if($_ =~ "^0\$")
{
 print "find\n";
}
else
{
 print "not find\n";
} 

result is:
not find
[download]

why regex can't match ? It looks like tachyon said "***This is not an RE***. " thanks!