A Recovery Mechanism for Shells

An undo facility is an essential component of most interactive applications. In current operating system shells, whether textual or graphical, such facilities are typically very poor. Algorithms are presented for adding a recovery mechanism to a shell which allows previous commands to be selectively undone and redone, and previous versions of files to be recovered. The recovery mechanism involves making the shell control resources in a more intelligent way. Programs are run under greater control, with the shell monitoring and analysing their resource requests. This provides better high-level information to the shell and, for example, provides techniques to prevent foreign or untrustworthy programs from doing any damage, and to reduce problems with conflicting resource requests from concurrent programs. A prototype implementation called brush has been constructed to investigate the convenience and natural feel of these facilities.