|Opening and Launching||Using 4Pane||FAQ|
This is 4Pane's substitute for MIME-types. You can get to the dialog by right-clicking a file and choosing "Open with...", or by double-clicking a file that has an extension unknown to 4Pane.
In the middle of the dialog is a tree of the applications that 4Pane knows about, stored in folders with names like Editors or Graphics. You can add more folders using the "Add Folder" button on the top right, and delete the currently-selected folder with the "Remove Folder" button. If a folder isn't empty, it has an Expand box to the left of its name. Clicking this opens it to show the names of the contained applications.
Select one of the folder's applications. You will see that its name is now displayed in the box at the top of the dialog, and the "Edit Application" button is now enabled. Clicking OK at this stage will open the file with that application just this once, without altering any settings.
To make persistent changes, click the "Edit Application" button. A new dialog appears, showing the settings for the application. You can alter any of these, but you will most often want to add or remove entries in the "Extension(s) that it should launch" box. This contains the extensions that this application can open e.g. txt for a text editor. If the application can cope with several different extensions, put them all here, separated by commas e.g. htm,html,HTM,HTML. Though I've called these entries 'extensions', and they almost always will be, you can actually put filenames there too if appropriate: for example, you might well want an editor to open "README" files, so enter txt,README,readme.
At the bottom of the dialog are two tickboxes. The first says "Open in terminal". A few applications will only work from a terminal, in which case tick this box. The other button, "Always use the selected application for this kind of file" does just that. If you tick this, the selected application will be used in the future if you double-click any file with this extension. Such extensions are displayed bold in the "Extension(s) that it should launch" box.
The other buttons at the top of the "Open With" dialog are "Remove Application", which does just that, and "Add Application", which launches a dialog similar to the "Edit Application" one just described.
That was all a bit confusing, so let me recap. You want an application to be associated with files having a particular extension, and so to appear on those files' context menu's "Open with..." submenu. Add that extension to the application's "Open With" dialog entry. If you want several applications to appear on the submenu, do this for each of them.
You want files having the extension "bar", when double-clicked, automatically to open in an application called "foo". Make sure that foo has an entry in the dialog, and the entry contains the extension bar. Then tick the entry's "Always use the selected application for this kind of file" box.