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Purpose: some gentle introductory examples of Tk

 #! /usr/local/bin/wish8.1
 button .hello -text "Hello, World!" -command { exit }
 pack .hello

These two lines place a clickable button on the screen, labeled "Hello, World", and the application terminates when the button is clicked.

Here's a slightly more useful variation: the button displays a counter that is incremented every time the button is clicked:

 #! /usr/local/bin/wish8.1
 button .b -text 0 -command {.b config -text [expr [.b cget -text]+1]}
 pack   .b ;#RS
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The explanation of the second example is this:

   * Create a button called .b
   * Initialize its text to the value zero
   * When the button is clicked, execute the following command.
   1. Change the text of the .b button.  The new value is calculated as follows.
   1. Get the current value of the button, and using expr, add 1 to that value.
   * The pack statement is what Tk uses to cause a widget to appear on the screen.
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'''JDG''':  Here's a different approach to the second example---it uses
the -textvariable arg:

 set foo 0
 button .b -textvariable foo -command { incr foo }
 pack .b

Again, a different approach---useful under different circumstances
(I find myself using -textvariable a *LOT* ... that's why I threw
this in).  --jdg [RS]: You're right, this is better. I considered it too but wanted to write a one-liner - until I saw that I'd need the #! line too... Point taken.
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'''KBK''': If you ever encounter a system in which the #! line
doesn't work, then try the following (for explanation, see [exec magic]):

 #! /bin/sh
 # next line is executed by the shell, but a comment in tcl \
 exec /path/to/wishM.N "$0" ${1+"$@"}

 set foo 0
 button .b -textvariable foo -command { incr foo }
 grid .b


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If the #! doesn't work, then it is unlikely that the above trick
will work either.  On the other hand, if #! does work , but the
path to the wish is so long that it is causing some heartburn to
your shell, then the above mentioned trick works.

However, that seems out of context for this page...