Use the regex to untaint the user-entered string: 

my $GOOD_NAME = qr/^(us\w*)/i;

my ( $accepted_name ) = $entered_un =~ /$GOOD_NAME/
    or die "Unacceptable input: $entered_un";

$sql = "select name, pass from unpw where name = '$accepted_name'";

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In reply to Re: Secure Regular Expression Check by Narveson
in thread Secure Regular Expression Check by Anonymous Monk

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