The shell script which is generated by screen is a simple but complete stand-alone program. It paints the screen, uses cursor to move around the screen and prompts the user for input.

screen can be used as a form entry to a table; it can be modified so that its output appended to a table or sent through a pipe; it can read in data and display on the screen; and validation can be added to check user input.

Follow these steps to set up an executable shell program using screen:

1.

Create a form file.

2.

Run screen using the form file created as input to generate a shell program.

3.

Execute the shell program to input data and output table.

4.

If desired, customize the shell program to validate, lock records, etc.

$ cat mail.f

                   Mail List Entry Form
                 <!date!>

Name  : <Name>             Company: <Company>
Street: <Street>
City  : <City>             State  : <State>       ZIP: <ZIP>
Phone : <Phone>

Everything prints on the screen except what is in angle brackets (< >), which are positions at which variables are read in. Commands surrounded by exclamation marks and angle brackets such as <!date!> are executed when the program is running.

$ screen < mail.f > mail.s
$ cat mail.s

: paint crt screen
exec 3>&1 1>&2
clear
cat <<SCREEN
                    Mail List Entry Form

 

Name  :                    Company:
Street:
City  :                    State  :               ZIP:
Phone :

SCREEN

: read user input
cursor  01 23 ; date;
cursor  03 08 ; read Name;
cursor  03 36 ; read Company;
cursor  04 08 ; read Street;
cursor  05 08 ; read City;
cursor  05 36 ; read State;
cursor  05 55 ; read ZIP;
cursor  06 08 ; read Phone;

: output table head
exec 1>&3
echo "Name  Company  Street  City  State  ZIP  Phone"
echo "----  -------  ------  ----  -----  ---  -----"
: append row
echo "$Name  $Company  $Street  $City  $State  $ZIP  $Phone"

The resulting shell progam is in three parts. First, the "paint crt screen" section will put the form on the screen after clearing the screen. Second, the "read user input" section will move the cursor to each input field and wait for the user to enter a string of characters which will be assigned to the column variables. Third, the "output table head" section will write out the user input to a table on the standard output.

The exec command sends the screen output to the screen through the third file descriptor, "standard error output," so that the screen program can be used in a pipe. For example, the table can be piped into another program. The "standard error" is usually unbuffered, speeding up output to the screen.

To execute mail.s, first make it executable with the chmod command.

$ chmod +x mail.s
$ mail.s > mail.t
                           Mail List Entry Form
                      Wed Sep  4 14:09:30 EDT 1992

Name  : Hi Ho              Company:
Street: 1st St.
City  : LA                 State  : CA            ZIP: 90024
Phone : 213-555-1212

$ cat mail.t
Name    Company Street  City    State   ZIP     Phone
----    ------- ------  ----    -----   ---     -----
Hi Ho   HH Inc. 1st St. LA      CA      90024   213-555-1212

The table output can be directed to a file or pipe. Here it was directed into a table named mail.t.