In RISC OS and the ROX Desktop, an application directory is a grouping of software code, help files and resources that together comprise a complete software package but are presented to the user as a single file. They also form the basis of the Zero Install application distribution system and are similar to the NEXTSTEP, GNUstep and Mac OS X concept of bundles. Their heritage lies in the system for automatically launching software stored on floppy disk on Acorn's earlier 8bit micros such as the BBC Micro.

Joining various files in this manner allows tools for manipulating applications to be merged with tools for manipulating the file system.

Fixed Contents

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In order to support user interaction with application directories, several files have special status.

Application binaries

Launching an application directory causes the included file AppRun (ROX Desktop) or !Run (RISC OS) to be launched. On RISC OS this is generally an Obey file (a RISC OS command script) which allocates memory and loads OS extension modules and shared libraries before executing the application binary. Under the ROX Desktop, it is not uncommon for it to be a shell script that will launch the correct system binary if available or compile a suitable binary from source otherwise.

Help files and icons

Both RISC OS and the ROX Desktop allow the user to view help files associated with an application directory without launching the application. RISC OS relies on a file in the directory named !Help in a proprietary format, while the ROX Desktop looks for HTML format help files in a Help directory.

Similarly, custom icons for the Application Directory may be contained within it - either .DirIcon (in PNG format) or AppIcon.xpm under the ROX Desktop, or !Sprites and optionally !Sprites22 under RISC OS.

!Boot

RISC OS application directories may contain a file named !Boot which is executed by the OS when the bundle is first discovered by the OS, allowing an application to do tasks such as register supported filetypes, or load different icons such as ASprites (icons with an alpha channel for RISC OS Select) or 5Sprites (icons with a RISC OS 5 appearance). !Boot files are the most popular propagation vector for such RISC OS viruses as exist (such as the well-known Extend virus). This feature is not duplicated by the ROX Desktop.

External links

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• ROX-Filer User Manual: Application directories