In computing, <code>ATTRIB</code> is a command in Intel ISIS-II, DOS, IBM OS/2, Microsoft Windows and ReactOS that allows the user to change various characteristics, or "attributes" of a computer file or directory. The command is also available in the EFI shell.
Several operating systems provided a set of modifiable file characteristics that could be accessed and changed through a low-level system call. For example, as of release MS-DOS 4.0, the first six bits of the file attribute byte indicated whether or not a file was read-only (as opposed to writeable), hidden, a system file, a volume label, a subdirectory, or if the file had been "archived" (with the bit being set if the file had changed since the last use of the <code>BACKUP</code> command). However, initial releases of the operating system did not provide user-level method for reading or changing these values.
The initial version of the <code>ATTRIB</code> command for DOS was first included in version 3.0 of PC DOS, with functionality limited to changing the read-only attribute. Subsequent versions allowed the read-only, hidden, system and archive bits to be set. MS-DOS version 3.3 added the capability of recursive searching through subdirectories to display attributes of specified files.
Digital Research DR DOS 6.0 and Datalight ROM-DOS also include an implementation of the command.
The FreeDOS version was developed by Phil Brutsche and is licensed under the GPLv2.
Setting the read-only bit of a file provided only partial protection against inadvertent deletion: while commands such as <code>del</code> and <code>erase</code> would respect the attribute, other commands such as <code>DELTREE</code> did not. Changing the system attribute was not possible in early versions of Windows, thus requiring use of <code>ATTRIB</code>. Similarly, a system crash in early versions of Windows could lead to a situation where a temporary file had the read-only bit set and was additionally (and irrevocably) locked by the Windows OS; in this instance, booting into DOS (thus avoiding the Windows lock) and unsetting the read-only attribute with <code>ATTRIB</code> was the recommended way of deleting the file. Manipulating the archive bit allowed users to control which files were backed up using the <code>BACKUP</code> command.