I like Gramp's solution: simple, elegant and efficient. Too often people automatically go for a regex when the good old tr operator is a better choice.

Due to my unfortunate golfing past, I can't restrain myself from noting that, if you are feeling in a silly mood, you could replace his simple and clear line:

print "Matched $_\n" if tr/pP// && tr/eE// && tr/rR// && tr/lL//;
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with this silly one:

y&pP&&&&y&eE&&&&y&rR&&&&y&lL&&&&print"Matched $_\n";
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Deparse confirming their equivalence:

# cat sensible.pl
print "Matched $_\n" if tr/pP// && tr/eE// && tr/rR// && tr/lL//;

# perl -MO=Deparse sensible.pl
print "Matched $_\n" if tr/Pp// and tr/Ee// and tr/Rr// and tr/Ll//;
sensible.pl syntax OK

# cat silly.pl
y&pP&&&&y&eE&&&&y&rR&&&&y&lL&&&&print"Matched $_\n";

# perl -MO=Deparse silly.pl
print "Matched $_\n" if tr/Pp// and tr/Ee// and tr/Rr// and tr/Ll//;
silly.pl syntax OK
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