eval string is also useful for loading modules dynamically e.g.

...
my $q = CGI->new;

my %modules = (
  simple => 'Filter::Simple',
  hard   => 'Filter::Util::Call'
);

my $filter = $q->param("filter");
if(exists $modules{$filter}) {
    eval "require $modules{$filter}";
}
...
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Without eval, you would have to convert the module name to a file path before passing it to require.