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#### A.10.1.17 Execute Code

Configuration for Execute Code action

The Execute Code action can execute arbitrary code using the expression language described in Section 7. Most of the expressions and functions just evaluate an expression, and in that case the only effect is that the result of the expression is displayed in the Results panel at the bottom of the activation window every time a row is activated. However, some functions are defined especially for use in this window, and have some additional effect such as popping up a viewer window, writing output to the console, or downloading a file. These are listed below.

In principle, this window can provide very flexible options for defining your own activation actions. In practice, the available activation functions don't give you much more sophisticated options than what is available in the other activation types. However, some more flexible options may be added in the future, and it is also possible to implement your own as explained in Section 7.11. Note that another option for configuring your own custom actions is to use the Run System Command to invoke a shell script or similar with supplied arguments.

Configuration:

Executable Expression
  Type in the expression to be evaluated on row activation. Column names act as variables which evaluate to the column value at the activation row, as explained in Section 7. The result of the expression is displayed in the Activation Window Results panel, but there may be other effects as well depending on the functions invoked. The expression is parsed as it is typed in, and if the current text does not represent a legal expression, the action is disabled, and an error message is displayed in the Status panel that should help to understand what's wrong.
Synchronous
  This checkbox determines whether the expression is evaluated on the Java Event Dispatch Thread or not. You can usually leave it alone, but if the expression is known to be fast to evaluate, multiple evaluations may behave a bit more predictably with it checked. For slow expressions, it should be unchecked (its default state).

The available Activation Functions (ones that have some effect other than just returning a value) are summarised below, and listed in detail in Appendix B.2. You can also browse them interactively in the Activation Functions branch of the Available Functions Window. Note some of these offer rather out of date functionality, and may be withdrawn (replaced by better alternatives) in future releases.

BasicImageDisplay
  Functions for display of graphics-format images in a no-frills viewing window (an `ImageWindow`).
Browsers
  Displays URLs in web browsers.
Image
  Functions for display of images in a window.
Mgc
  Specialist functions for use with data from the the Millennium Galaxy Survey.
Output
  Functions for writing text to standard output.
Sdss
  Specialist display functions for use with the Sloan Digital Sky Server.
SuperCosmos
  Specialist display functions for use with the SuperCOSMOS survey.
System
  Functions for executing shell commands on the local operating system and other system-level operations.
TwoQZ
  Specialist functions for use with data from the the 2QZ survey.

Invoking certain activation functions configured by an unknown party has security implications. If this action is loaded from a session file, the security panel will be shown.

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk