I think rejecting any $str containing anything which isn't a cipher, comma or dot prior to eval $str should be good enough

  DB<53> $EVIL= ',@{[say "kill all kitties!"]}'

  DB<54> $str = "2,4..9"

  DB<55> p $str =~ m/[^0-9,.]/           # OK

  DB<56> $str .= $EVIL

  DB<57> p $str =~ m/[^0-9,.]/           # NOT OK
1
  DB<58> eval $str
kill all kitties!

[download]

update

in order to avoid syntax error you need to check $@ to see if the eval was successful. NB line 82, not all errors are caught tho

  DB<80> @list = eval ",1..3"; unless($@){say for @list }

  DB<81> @list = eval "1..3"; unless($@){say for @list }
1
2
3

  DB<82> @list = eval "1.3"; unless($@){say for @list }
1.3

[download]

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

In reply to Re^4: loop iterator in a string by LanX
in thread loop iterator in a string by Anonymous Monk

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