[Tk]'s radiobutton widget documentation can be found at
http://purl.org/tcl/home/man/tcl8.4/TkCmd/radiobutton.htm
while [Ttk]'s radiobutton widget documentation can be found at
http://www.tcl.tk/man/tcl8.5/TkCmd/ttk_radiobutton.htm .

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'''Tk Example:'''

Radio buttons are linked using a common variable, which will have the value of the selected button.

 package require Tk

 set ::onetwothree "3"

 pack [radiobutton .one   -value 1 -text "One"   -variable onetwothree -command { puts $::onetwothree }]
 pack [radiobutton .two   -value 2 -text "Two"   -variable onetwothree -command { puts $::onetwothree }]
 pack [radiobutton .three -value 3 -text "Three" -variable onetwothree -command { puts $::onetwothree }]

The results will be that, on stdout, the number of the radiobutton pressed
is output.

Also note that by setting the variable to 3, the 3rd radio button is selected
at the beginning of the code.  

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[rdt] As an example, this is (of course) correct code, but in this case is there ever a time which you would not want to have the "-anchor w" argument to the pack command to align the buttons?
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See the ''vertical'' command, which allows to place the text below the checkfield, on the [checkbutton] page.

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'''See also'''

   * [Lightbutton] a pure Tcl package mimicking the radio and the checkbuttons, with bright and pretty colors.

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[Category Widget] - [Category Command] - [Tk syntax help] - [Arts and Crafts of Tcl-Tk Programming]