Solution:
If you have $ in you string use single quotes:
display('$vhkvdov#jqlydk#p*_L#1qrlws|ufqh#KWLZ#1hwdgsX');
Otherwise PHP would try to use $vhkvdov as a variable name and replace it by its contents, what will be nothing as I expect that the variable is not set
Note: During development I would set error_reporting in php.ini to
error_reporting=E_ALL | E_NOTICE;
and
display_errors=On
or
log_errors=On
error_log=PATH/TO/YOUR/LOG.file ; make sure this is writable by the web server
To see an error message like :
PHP Notice: Undefined variable: vhkvdov in