Drop eval STRING; use eval BLOCK:

eval {
    my $file = 'foo.pl';
    require $file;
};
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As broquaint points out, $file will be interpolated into the string before the eval runs. To see what you're really doing, try this:

my $notwhatiwant = qq{
    $file = 'foo.pl'; # foo has errors in it
    require "$file";
};

print "<$notwhatiwant>\n";
eval $notwhatiwant;
dienice("that code is busted because: $@") if $@;
[download]

I think you'll be surprised.