Purpose: some gentle introductory examples of Tk
======
#! /usr/local/bin/wish8.5
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/wish8.5
button .b -text 0 -command {.b config -text [expr {[.b cget -text]+1}]}
pack   .b ;#RS
======
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.
   ** Change the text of the `.b` button.  The new value is calculated as follows.
   *** 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.
----

'''JDG''':  Here's a different approach to the second example — it uses the '''-textvariable''' option:
======
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
<<br>>
[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.
----
'''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/wish'''M'''.'''N''' "$0" ${1+"$@"}

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

[DKF]: Also consider:
===
#! /usr/bin/env wish'''M'''.'''N'''
set foo 0
grid [[button .b -textvariable foo -command {incr foo}]]
===
The `env` program is an ideal helper here, and I like creating and managing widgets on the same line.
----
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...
----
[CM]: Not really a ''program'', I admit.. but compared to the first script, we can reduce its length significantly by just typing:
===
'''$''' echo 'pack [[button .h -text "Hello, World!" -command exit]]' | wish8.5
===
This assumes, however that you are running Unix. In an MS-DOS shell, something like:
===
'''>''' echo pack [[button .h -text "Hello, World!" -command exit]] | "C:\Program Files\Tcl\bin\wish85.exe"
===
should work too. That's 70 bytes to type for a nice Hello World button! And it's ''easy to understand''! (for Perl lovers.. :-).

[DKF]: If your [PATH] environment variable is set right, that last one can be shortened to:
===
'''>''' echo pack [[button .h -text "Hello, World!" -command exit]] | wish85
===
----
What does this do under DOS, er windoze?
======
#\
exec wish $0
pack [button .h -text "Hello, World!" -command exit]
======
'''-PSE'''

[Peter Lewerin]: not very much.  Take a look at [DOS BAT magic] for a working solution.
----
!!!!!!
%| [Category Tutorial] |%
!!!!!!