Bash script function that changes the value of a variable

I'd like to make a function for a BASH script that changes the value of one of its arguments, that is a variable. The function that I did is: 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" ; } Then in some part of the script there is a dialog box asking you to insert a name and then this function checks if the given name is a valid name. For instance, 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=$chckd_var ; The problem I have is that the "output" of my function, the value I have now, is not in the same variable I used in the first place. I have to assign the value of the "output" of my function ($chckd_var) to the variable that I inserted as an argument in the function (user_name). What I want to do is that the function changes the value of the global variable user_name (or whatever other variable). Also, I'd like to know if there's a way to get the output of a dialog inputbox directly in a variable; not in a file. I'm fairly new to BASH scripts, so perhaps the answer is quite simple. Anyway, I've been looking for this on the web and haven't found the answer.