chck_rgx () { # Checks that the given name for a user/group fulfills the regex. The function's parameters are
              #   * $1: kind of name to check: username, hostname, etc.
              #   * $2: variable whose value to check if meets the requirements.
  local rgx_hostname='^[a-z][a-zA-Z0-9_-]+$' ;
  local rgx_inputbox_hostname="The hostname you just submitted isn't a valid name. Try with another name."
  local rgx_username='^[a-z][a-z0-9_-]+$' ;
  local rgx_inputbox_username="The username you just submitted isn't a valid name. Try with another name." ;
  eval rgx_name="$rgx_$1" ;
  eval rgx_inputbox="$rgx_inputbox_$1" ;
  eval name_ch="$$2" ;
  while [[ ! $name_ch =~ $rgx_name ]] ; do
    dialog --backtitle "$backtitle_var"
           --title     "Wrong $1 submitted" --clear
           --inputbox  "$rgx_inputbox" 0 0 2> name-ch ;
    name_ch=$(cat name-ch) ;
    rm name-ch ;
  done
  chckd_var="$name_ch" ;
}

dialog  --backtitle "$backtitle_var"
        --title     "Submit the username" --clear
        --inputbox  "Which username do you want?" 0 0 2> user-name ;
user_name=$(cat user-name) ;
chck_rgx username user_name ;
user_name=$chckd_var ;