GAMBAS-BOOK 3.19.5

You are sure to know how to start programs with parameters in the console. The following command starts the editor program' gedit', opens the file' set_color. sh' in the home directory and places the cursor in line 5 at the 9th position:

hans@linux:~$ gedit ./set_color.sh +5:9

The function of the presented program (bash script)' set_color. sh' consists of assigning values internally to the parameters $1 to $3 via the command' let' 3, depending on the number of parameters passed, and then assigning values to the variables R, G and B or the variables R, G and B with the values of the exactly 3 passed parameters. A (colour) value is then calculated and displayed with the variables R, G and B.

#!/bin/bash
#
if [ $# -ne 3 ]		# If the number of parameters is not equal to 3, then ...
  then
    set 220 20 180 	# → $1=220 , $2=20 , $3=180
    R=$1
    G=$2
    B=$3
  else
    R=$1
    G=$2
    B=$3
fi
let color=$R*256*256+$G*256+$B
echo colour value = $color
echo Continue with ENTER...
read dummy

In general:

• $1 to $k form a parameter list of the passed parameters, in which the order also corresponds to a ranking order.
• The first argument $0 contains the name of the started program.
• The value of $# returns the number of parameters $1… $k passed.

The script' set_color. sh' is started first with exactly three parameters and then only with two parameters. The parameters are not checked for validity in the context of RGB color values:

hans@linux:~$ chmod +x set_color.sh # Make the script executable

hans@linux:~$ ./set_color.sh 10 20 128
Colour value = 660608
Continue with ENTER...

hans@linux:~$ $HOME/set_color.sh 0 128
Colour value = 14423220
Continue with ENTER...

Of course, you can also start a Gambas program with parameters in a console:

hans@linux:~$ gbx3 $HOME/color_select -- 225 110 60
hans@linux:~$ gbx3 ./color_select -- 225 110 60
hans@linux:~$ gbr3 $HOME/color_select/color_select.gambas -- 225 110 60

As a separator between the Gambas project path and the arguments,“–” is used. This is also indicated in the help of gbx3: Usage: gbx3[options][<project file>] [– <arguments>]/, if <arguments> is interpreted as a placeholder for a parameter list separated by blanks.

With Application. Args, Gambas provides an array with the given arguments of the program from the console. The first argument Application. Args[0] is (? $0) is always the name of the started Gambas program and the property Application. Args. Count returns the number of all - not only the passed - parameters. In this point, working with the array of arguments in Gambas differs from determining the number of arguments in a bash script, because the source code of the Gambas project' color_select' is similar to the above-mentioned bash script. With the values of the 3 parameters - which are not checked in this variant - a color value is calculated, which serves as default value for the used component ColorChooser1:

Public Sub Form_Open()
 
  Dim R, G, B As Integer
 
  FColor.Center
  FColor.Resizable = False
 
  If Application.Args.Count <> 4 Then
     R = 220
     G = 20
     B = 180
  Else
     R = Val(Application.Args[1])
     G = Val(Application.Args[2])
     B = Val(Application.Args[3])
  Endif '  Application.Args.Count <> 4 ?
 
  ColorChooser1.Value = Color.RGB(R, G, B)
 
End ' Form_Open

The call:

hans@linux:~$ gbx3 ./color_select -- 33 133 33

starts the program for color selection with the default color medium-green:

Figure 5.3.3.2.1: Color selection program - default color via 3 parameters

The following modified section of the source code contains a check of the parameter values:

Public Sub Form_Open()
  Dim sMessage As String
 
  FColor.Center
  FColor.Resizable = False
 
  If Application.Args.Count <> 4 Then
     ColorChooser1.Value = Color.RGB(220, 20, 180) ' Colour: pink
  Else
     If ParameterTest(Application.Args[1], Application.Args[2], Application.Args[3]) = True Then
        ColorChooser1.Value = Color.RGB(Val(Application.Args[1]), Val(Application.Args[2]),
        Val(Application.Args[3]))
     Else
        sMessage = "At least one parameter has a wrong value!"
        sMessage &= gb.NewLine
        sMessage &= "Parameterliste: " & Application.Args[1] & Chr(32) & Application.Args[2] & Chr(32) &
                    Application.Args[3]
        sMessage &= gb.NewLine
        sMessage &= "The programme will be terminated immediately!"
        Message.Error(sMessage)
        FColor.Close
     Endif
  Endif ' Application.Args.Count = 4 ?
 
End ' Form_Open
 
Public Function ParameterTest(p_1 As String, p_2 As String, p_3 As String) As Boolean
  Dim bOK As Boolean
 
  If IsInteger(p_1) = True And IsInteger(p_2) = True And IsInteger(p_3) = True Then
     If (Val(p_1) >= 0) And (Val(p_1) <= 255) Then
        bOK = True
     Else
        bOK = False
     Endif
     If (Val(p_2) >= 0) And (Val(p_2) <= 255) Then
        bOK = True
     Else
        bOK = False
     Endif
     If (Val(p_3) >= 0) And (Val(p_3) <= 255) Then
        bOK = True
     Else
        bOK = False
     Endif
  Else
     bOK = False
  Endif
 
  Return bOK
 
End ' Function ParameterTest(...) As Boolean

This follows a call of the program in the console:

hans@linux:~$ gbx3 ./color_select -- 128 128 294

this error message:

Figure 5.3.3.2.2: Error message - 294 ∉ [0…255]