How to add the symbols [ ] in the field nickname ?

How to add the symbols [ ] in the field nickname ?

return ( preg_match( '/^[a-zA-Z0-9_{}()-]+$/', $arg0 ) and !file_exists( $dir['root'] . $arg0 ) );

Currently I have this expression . I would also like to allow brackets [ ]

try this and let me know

return ( preg_match( '/^[a-zA-Z0-9_{}()-\[\]]+$/', $arg0 ) and !file_exists( $dir['root'] . $arg0 ) );

Thx.

Works well. 

With that form he accepts the . , ;

How can I do that I do not accept the . , ; but yes [] () {}

Thx

Try this one:

return ( preg_match( '/^[a-zA-Z0-9_\[\]\(\)\{\}-]+$/', $arg0 ) and !file_exists( $dir['root'] . $arg0 ) );