Linux Shell Scripting Tutorial (LSST) v1.05r3
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User Interface and dialog utility-Part I

Good program/shell script must interact with users. You can accomplish this as follows:
(1) Use command line arguments (args) to script when you want interaction i.e. pass command line args to script as : $ ./sutil.sh foo 4, where foo & 4 are command line args passed to shell script sutil.sh.
(2) Use statement like echo and read to read input into variable from the prompt. For e.g. Write script as:

$ cat > userinte
 #
 # Script to demo echo and read command for user interaction
 #
 echo "Your good name please :"
 read na
 echo "Your age please :"
 read age
 neyr=`expr $age + 1`
 echo "Hello $na, next year you will be $neyr yrs old."

Save it and run as
$ chmod 755 userinte
$ ./userinte
Your good name please :
Vivek
Your age please :
25
Hello Vivek, next year you will be 26 yrs old.

Even you can create menus to interact with user, first show menu option, then ask user to choose menu item, and take appropriate action according to selected menu item, this technique is show in following script:

$ cat > menuui
 #
 # Script to create simple menus and take action according to that selected
 # menu item
 #
 while :
  do
     clear
     echo "-------------------------------------"
     echo " Main Menu "
     echo "-------------------------------------"
     echo "[1] Show Todays date/time"
     echo "[2] Show files in current directory"
     echo "[3] Show calendar"
     echo "[4] Start editor to write letters"
     echo "[5] Exit/Stop"
     echo "======================="
     echo -n "Enter your menu choice [1-5]: "
     read yourch
     case $yourch in
       1) echo "Today is `date` , press a key. . ." ; read ;;
       2) echo "Files in `pwd`" ; ls -l ; echo "Press a key. . ." ; read ;;
       3) cal ; echo "Press a key. . ." ; read ;;
       4) vi ;;
       5) exit 0 ;;
       *) echo "Opps!!! Please select choice 1,2,3,4, or 5";
          echo "Press a key. . ." ; read ;;
  esac
 done

Above all statement explained in following table:

Statement	Explanation
while :	Start infinite loop, this loop will only break if you select 5 ( i.e. Exit/Stop menu item) as your menu choice
do	Start loop
clear	Clear the screen, each and every time
echo "-------------------------------------" echo " Main Menu " echo "-------------------------------------" echo "[1] Show Todays date/time" echo "[2] Show files in current directory" echo "[3] Show calendar" echo "[4] Start editor to write letters" echo "[5] Exit/Stop" echo "======================="	Show menu on screen with menu items
echo -n "Enter your menu choice [1-5]: "	Ask user to enter menu item number
read yourch	Read menu item number from user
case $yourch in 1) echo "Today is `date` , press a key. . ." ; read ;; 2) echo "Files in `pwd`" ; ls -l ; echo "Press a key. . ." ; read ;; 3) cal ; echo "Press a key. . ." ; read ;; 4) vi ;; 5) exit 0 ;; *) echo "Opps!!! Please select choice 1,2,3,4, or 5"; echo "Press a key. . ." ; read ;; esac	Take appropriate action according to selected menu item, If menu item is not between 1 - 5, then show error and ask user to input number between 1-5 again
done	Stop loop , if menu item number is 5 ( i.e. Exit/Stop)

User interface usually includes, menus, different type of boxes like info box, message box, Input box etc. In Linux shell (i.e. bash) there is no built-in facility available to create such user interface, But there is one utility supplied with Red Hat Linux version 6.0 called dialog, which is used to create different type of boxes like info box, message box, menu box, Input box etc. Next section shows you how to use dialog utility.


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