I have a Single Line field "FIELD" that has to contain only digit [0-9] and not contain any other character.

Reading other post on the Forum I understand that there is no way to define a mask but on Validate section I can write a Script.

The 

if (FIELD  .matches("[0-9]"== false)

...does not work.

I don't know the exact number of digit to input in FIELD.

Can You help me?

tks

Pippo