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$ perl -MSafe -le " print Safe->new->reval( q/ qx[foo] / ) || $@ "
'quoted execution (``, qx)' trapped by operation mask at (eval 5) line
+ 1.
...
$ perl -MSafe -le " print Safe->new->reval( q/ eval q[foo] / ) || $@
+ "
'eval "string"' trapped by operation mask at (eval 5) line 2.