perldoc perlsec
It would be inefficient for every operator to test every argument for taintedness. Instead, the slightly more efficient and conservative approach is used that if any tainted value has been accessed within the same expression, the whole expression is considered tainted. 
#!/usr/bin/perl -T
$ENV{PATH} = '/usr/bin:/usr/local/bin:/bin';
$ENV{ENV} = '';
my $good = 'good';
my $bad = `echo bad`;
print($bad); print(`echo $good`); #separate expressions
print($bad), print(`echo $good`); #single list expression

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In reply to Re: Re: Re: Taint bug with backticks in variable assignments by Anonymous Monk
in thread Taint bug with backticks in variable assignments by shotgunefx

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