perl -T your_script [args...]

##</code><code>##

$sql = "select * from some_table where some_col = $target";
$sth = $dbh->prepare( $sql );
$sth->execute;
...

##</code><code>##

$sql = "select * from some_table where some_col = ?";
$sth = $dbh->prepare( $sql );
$sth->execute( $target );

##</code><code>##

$sql = "select $colum from $table";

##</code><code>##

my $cols = ( foo => 'foo', bar => 'bar', baz => 'baz' );
my $tbls = ( parts => 'parts', table2 => 'table2' );

my $inp_col = <USER>;  # get data from untrusted sources
my $inp_tbl = $ENV{TABLE};

if ( exists( $cols{$inp_col} ) and exists( $tbls{$inp_tbl} ) {
   my $sql = "select $cols{$inp_col} from $tbls{$inp_tbl}";
   # now it's safe to run the query...
}