If $string is "a", then \/$string\/[a-z]* does NOT match "air". It would match "/a/ir".

$string = "a";
print "success 1\n" if "air"   =~ /$string/;
print "success 2\n" if "air"   =~ /\/$string\/[a-z]/;
print "success 3\n" if "/a/ir" =~ /\/$string\/[a-z]/;
print "success 4\n" if "air"   =~ /$string[a-z]/;      # UPDATE
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