If zcat throws an error then you know it's not gzipped: 
open(FOO, "zcat $foo |") || open(FOO, $foo) || die("ERROR: Unable to o
+pen file $foo for read: $!");

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In reply to Re: How to test if a file is gzipped or not by Anonymous Monk
in thread How to test if a file is gzipped or not by Special_K

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