Both dragonchild and Roy Johnson say that you should be looking at qr// and while I agree, you might want to be careful about how you use it if you're also using regular expression modifiers. For instance,

perl -le '$re = "(hello)"; $_ = "Hello world";  print $1 if /$re/i;'
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works just fine, but

perl -le '$re = qr/(hello)/; $_ = "Hello world";  print $1 if /$re/i;'
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won't.

You need to put the modifier with the qr// for it to be interpretted correctly. I.e.,

perl -le '$re = qr/(hello)/i; $_ = "Hello world";  print $1 if /$re/;'
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Just a note in case it comes up :-)