codice:
 <input type="file" name="allegato" onkeyup="this.value=this.value.replace(/'/g,'_').replace(/\./,'_').replace(/[^\d_]/g,'').replace(/_/,'.').replace(/^\./,'').replace(/_/,'');" onblur="this.value=this.value.replace(/'/g,'_').replace(/\./,'_').replace(/[^\d_]/g,'').replace(/_/,'.').replace(/^\./,'').replace(/_/,'');"onchange="this.value=this.value.replace(/,/g,'.').replace(/\./,'_').replace(/[^\d_]/g,'').replace(/_/,'.').replace(/^\./,'').replace(/\.$/,'').replace(/_/,'');">
questo non funziona