You'll find the answer to this in perldoc perlop

Update: Corrected 2nd example. (thanks lidden & bart)

=~ binds a scalar expression to a pattern match, eg: 

print "Matches!" if "hello" =~ m/he/;

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The period (.) is a concatenation operator. When used in conjunction with = it concatenates the right argument to the left argument. For example.. 
($foo = "hello") .= " world";
# or
$foo = "hello"; $foo .= " world";

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Is the same as.. 
$foo = "hello world";

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Cheers,
Darren :)

In reply to Re: Explaining =~ and .= operators by McDarren
in thread Explaining =~ and .= operators by Thelonius Monk

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