Thanks all for the input.
crashtest, i use:

use FindBin;
use lib "$FindBin::Bin/PathWithModulesOfMyApp";
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so i don't need to have "/" or "\" in $op, that's why the regexp is so strict. The reason to ask, is that imho "require" makes a BIG securiry issue, when the regexp is missing, you'd be able to do things like this

http://127.0.0.1/cgi-bin/script.pl?option=%60touch%20/tmp/HA_I_CAN_WRI
+TE_ON_YOUR_HARDDISK.txt%60
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and think of more nasty things to do.
That's what Tanktalus warns about, and that's why i'm wondering if there is a way to avoid the use of eval totally.
I'll have a look at UNIVERSAL::require and Class::Inspector as well, more options are welcome.