If a file name is not an absolute path name, it is considered to be relative to base-directory as given on the command line. The base-directory parameter must be a simple absolute pathname (it must not contain multiple consecutive slashes or references to the special directories "." or "..").

fastrm is designed to be faster than the typical "| xargs rm" pipeline when given a sorted list of file names as input. For example, fastrm will usually (2) into a directory before removing files from it, meaning that if its input is sorted, most names passed to (2) will be simple names. This can substantially reduce the operating system overhead from directory lookups.

fastrm assumes that its input is valid and that it is safe to call (2) on every file name it is given. As a safety measure, however, fastrm when running as root will check with (2) that a file name doesn't specify a directory before removing it. (In some operating systems, root is allowed to unlink directories, even directories which aren't empty, which can cause file system corruption.)

The input to fastrm should always be sorted --- or even better be in the order file names are output by find(1) --- if speed is an issue and the input isn't solely storage API tokens. (It deals fine with unsorted input, but is unlikely to be any faster in that case than a simple "xargs rm" command.) Sorting may even slightly speed up the removal of storage API tokens due to caching effects, since sorting will tend to keep all of the tokens from a particular storage method together.

Various additional optimizations for removing files can be turned on and/or tuned with options (see below). Which options will be most effective depends heavily on the underlying structure of the file system, the way in which directories are stored and searched, and similar, often underdocumented, operating system implementation details. The more sophisticated the underlying operating system and file system, the more likely that it will already perform the equivalent of these optimizations internally.