Re: Small examples of string eval

[ruzam]

I have two places where I use eval all the time. I think eval is the best choice in these situations, maybe someone has a better alternative (that doesn't require non-core modules).

1) retrieving stored hashes
I regularily used Data::Dumper to turn hashes into strings so they can be stored in a database for later retrieval. The string accurately represents the original hash with out my having to do a thing and it's safe to store anyway I have to, flat files, dbm, mysql. When the data is later retrieved, eval is the easiest way to get it back into a useful hash. Something like this:

use Data::Dumper;
$Data::Dumper::Indent = 0; # no spaces tabs or other fluff
$Data::Dumper::Purity = 1; # include code to recreate recursive refere
+nces

sub store_hash {
    my $hash_ref = shift;
    my $saved = Dumper($hash_ref);
    # store $saved somewhere
}

sub get_hash {
    # get $saved from somewhere
    my $VAR1;
    eval {$saved}
    return $VAR1 ? $VAR1 : {};
}

1) wrapping DBI calls to capture errors. Far as I know this is the recommended (only?) way to do this.

sub selectrow_array { my $dbh = shift;
    my $query = shift;
    my @result;
    eval { @result = $dbh->selectrow_array($query) };
    return my_custom_error_handler("selectrow_array $query") if $@;
    return @result;
}

More generically I guess you could say eval is the tool of choice when ever you have to call code beyond your control that may kill your script.