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On DOS, OS/2 and Windows, different programs called from their COMMAND.COM or CMD.EXE (or internal their commands) may use different syntax within the same operating system. For example: Options may be indicated by either of the switch characters: /, -, or either may be allowed. See below. They may or may not be case-sensitive.
After authentication, and if the configuration file permits the user access, the system invokes the requested command. sudo retains the user's invocation rights through a grace period (typically 5 minutes) per pseudo terminal, allowing the user to execute several successive commands as the requested user without having to provide a password again.
A command-line interpreter may offer a history function, so that the user can recall earlier commands issued to the system and repeat them, possibly with some editing. Since all commands to the operating system had to be typed by the user, short command names and compact systems for representing program options were common.
Command line shells on Windows usually use the Windows API to change the current working directory, whereas on Unix systems cd calls the chdir() POSIX C function. This means that when the command is executed, no new process is created to migrate to the other directory as is the case with other commands such as ls. Instead, the shell itself ...
In Linux, if the script was executed by a regular user, the shell would attempt to execute the command rm -rf / as a regular user, and the command would fail. However, if the script was executed by the root user, then the command would likely succeed and the filesystem would be erased. It is recommended to use sudo on a per-command basis instead.
The command su, including the Unix permissions system and the setuid system call, was part of Version 1 Unix.Encrypted passwords appeared in Version 3. [5] The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.
Support for command history means that a user can recall a previous command into the command-line editor and edit it before issuing the potentially modified command. Shells that support completion may also be able to directly complete the command from the command history given a partial/initial part of the previous command.
COMMAND.COM, the original Microsoft command line processor introduced on MS-DOS as well as Windows 9x, in 32-bit versions of NT-based Windows via NTVDM; cmd.exe, successor of COMMAND.COM introduced on OS/2 and Windows NT systems, although COMMAND.COM is still available in virtual DOS machines on IA-32 versions of those operating systems also.