Taintモードの振る舞い

Perl

Taintモードの振る舞いがよく分からない。

$ perl -Te 'eval "" if $^X'
Insecure dependency in eval while running with -T switch at -e line 1.

$ perl -Te 'require strict if $^X'
Insecure dependency in require while running with -T switch at -e line 1.

$ perl -Te 'my $s = $^X; require strict if $s'
Insecure dependency in require while running with -T switch at -e line 1.

$ perl -Te 'require strict if $^X ? 1 : 1'
Insecure dependency in require while running with -T switch at -e line 1.

$ perl -Te 'my $s = $^X ? 1 : 1; require strict if $s; print "OK\n"'
OK

とりあえず"require X::PurePerl if $ENV{X_PUREPERL}"がTaintモードの元でエラーになるのは確からしい。