Командные оболочки: история и разновидности

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A command shell is a command line interface to interact with and manipulate a computer's operating system.

ShellUsual environmentUsually invokedIntroducedPlatform independentDefault login shell inDefault script shell inLicenseSource code availabilityUser interfaceMouse supportUnicode supportISO 8601 supportConsole redirectionStream redirectionConfigurabilityStartup/shutdown scriptsBatch scriptsLoggingAvailable as statically linked, independent single file executableThompson shellUNIXsh1971UNIXUNIXText based CLIBourne shell 1977 version7th Ed. UNIXsh19777th Ed. UNIX7th Ed. UNIX,Text based CLIBourne shell current versionVarious UNIXsh1977SunOS 5. x, FreeBSDSunOS 5. xText based CLIPOSIX shellPOSIXsh1992POSIXText based CLIUnspecified ( given as an example)bash (v4)POSIXbash, sh1989GNU, Linux (default for root), macOS 10.3–10.14GNU, Linux, Haiku, macOS 10.3–10.14Text based CLIcshPOSIXcsh1978SunOSText based CLItcshPOSIXtcsh, csh1983FreeBSD (former default for root), formerly Mac OS XText based CLIHamilton C shellWin32, OS/2csh1988 (OS/2 version no longer maintained)Text based CLIScshPOSIXscsh1994ksh (ksh93t+)POSIXksh1983AIX, HP UXOpenSolarisText based CLIashPOSIXsh1989Minix, BusyBox based systemsNetBSD, Minix, BusyBox based systemsText based CLI (for BusyBox, supported in command line editing, but not in string handling)CCPCP/M, MP/M(CCP)1976 (1974)CP/M (no login), MP/MCP/M, MP/M (originally closed source)Text based CLI (automatic via ) (only via external command to update )COMMAND. COMDOSCOMMAND1980 (3rd party implementations, not bound to a specific DOS vendor or version, available)DOS, Windows 95, 98, SE, MEDOS, Windows 95, 98, SE, MEvendor specific, f. e. MS EULA, or BSD/GPL (free clones) (except for OpenDOS, DR DOS, PTS/DOS and FreeDOS)Text based CLI (except for DR DOS) (via or ) (via startup parameters and environment variables, DR DOS also supports user default switch command) (automatic for primary shell, or explicitly via , or startup options) (via command or and startup options)OS/2 CMD. EXEOS/2, eComStation, ArcaOSCMD1987OS/2, eComStation, ArcaOSOS/2, eComStation, ArcaOSText based CLI (only via startup option) (via command or and startup options)Windows CMD. EXEWin32CMD1993Windows NT, 2000, XP, Server 2003, VistaWindows NT, 2000, XP, Server 2003, VistaText based CLI ( for UTF 8, but program arguments are still encoded in local codepage) (via registry, startup parameters, and environment variables) (automatic via registry, or explicitly via startup option) (via command or and startup options)4DOS, NDOSDOS, Windows 95, 98, SE, ME4DOS, NDOS1989 (1986)Text based CLI with TUI extensions (popups, help system, internal variable, command) (via , except for , , , , , , , commands and file / directory coloring) (via / file, startup parameters, environment variables, command) (automatic for primary shell and / as well as / for any shell, or explicitly via , or startup options) (via command or and startup options)4OS2OS/2, eComStation, ArcaOS4OS21992 (but bundled with ArcaOS)Text based CLI (via file, startup parameters, environment variables, command) (automatic via / as well as / files, or explicitly via option) (via command or and startup options)TCC (formerly 4NT)Win32TCC1993optionaloptionalText based CLI (Take Command: GUI) (console mouse, popups, help system, , internal variables, command) (via registry, / file, startup parameters, environment variables, command) (automatic via registry and / as well as /, or explicitly via startup option) (via command or and startup options)VMS DCLOpenVMSAutomatically for login/interactive process1977?VMSVMSProprietary, bundled in VMSText based CLIPowerShell. NET,. NET FrameworkPowerShell2006Windows 10, 8, Server 2008, 7Windows 10, 8, Server 2008, 7Graphical CLIrcPlan 9, POSIXrc1989Plan 9, Version 10 UnixPlan 9, Version 10 UnixText based CLIBeanShellJava2005fishPOSIXfish2005GhostBSDText based CLIIonRedox, Linuxion2015RedoxRedoxText based CLI (not distributed as a standalone executable, but it can be built as one)ShellUsual environmentUsually invokedIntroducedPlatform independentDefault login shell inDefault script shell inLicenseSource code availabilityUser interfaceMouse supportUnicode supportISO 8601 supportConsole redirectionStream redirectionConfigurabilityStartup/shutdown scriptsBatch scriptsLoggingAvailable as statically linked, independent single file executable

ShellCommandnamecompletionPathcompletionCommandargumentcompletionWildcardcompletionCommandhistoryMandatoryargumentpromptAutomaticsuggestionsColoreddirectorylistingsTexthighlightingSyntaxhighlightingDirectory history, stack or similar featuresImplicitdirectorychangeAuto­correctionIntegratedenvironmentSnippetsValuepromptMenu/optionspromptProgressindicatorContextsensitivehelpCommandbuilderThompson shell? ?Bourne shell 1977 version? ?ExternalBourne shell current versionExternalcshExternaltcshExternalHamilton C shellExternalScsh? ?Externalksh (ksh93t+)ExternalpdkshExternalzshThird party extensionExternalashExternalCCPCOMMAND. COM (only in DR DOS through %$ON%, %$OFF%, %$HEADER%, %$FOOTER%) (only single stepping with COMMAND /Y (via , and commands) (via function, and indirectly via a combination of , , commands) (except for command for INI file directives)4OS2?????? ?TCC (formerly 4NT) (via , , and commands) (via function, and indirectly via a combination of , , commands)PowerShellShellCommandnamecompletionPathcompletionCommandargumentcompletionWildcardcompletionCommandhistoryMandatoryargumentpromptAutomaticsuggestionsColoreddirectorylistingsTexthighlightingSyntaxhighlightingDirectory history, stack or similar featuresImplicitdirectorychangeAuto­correctionIntegratedenvironmentSnippetsValuepromptMenu/optionspromptProgressindicatorContextsensitivehelpCommandbuilder

Background execution allows a shell to run a command without user interaction in the terminal, freeing the command line for additional work with the shell. POSIX shells and other Unix shells allow background execution by using the & character at the end of command. In PowerShell, the Start Process or Start Job cmdlets can be used.

Completion features assist the user in typing commands at the command line, by looking for and suggesting matching words for incomplete ones. Completion is generally requested by pressing the completion key (often the key). Command name completion is the completion of the name of a command. In most shells, a command can be a program in the command path (usually $PATH), a builtin command, a function or alias. Path completion is the completion of the path to a file, relative or absolute. Wildcard completion is a generalization of path completion, where an expression matches any number of files, using any supported syntax for file matching. Variable completion is the completion of the name of a variable name (environment variable or shell variable). Bash, zsh, and fish have completion for all variable names. PowerShell has completions for environment variable names, shell variable names and — from within user defined functions — parameter names. Command argument completion is the completion of a specific command's arguments. There are two types of arguments, named and positional: Named arguments, often called options, are identified by their name or letter preceding a value, whereas positional arguments consist only of the value. Some shells allow completion of argument names, but few support completing values. Bash, zsh and fish offer parameter name completion through a definition external to the command, distributed in a separate completion definition file. For command parameter name/value completions, these shells assume path/filename completion if no completion is defined for the command. Completion can be set up to suggest completions by calling a shell function. The fish shell additionally supports parsing of man pages to extract parameter information that can be used to improve completions/suggestions. In PowerShell, all types of commands (cmdlets, functions, script files) inherently expose data about the names, types and valid value ranges/lists for each argument. This metadata is used by PowerShell to automatically support argument name and value completion for built in commands/functions, user defined commands/functions as well as for script files. Individual cmdlets can also define dynamic completion of argument values where the completion values are computed dynamically on the running system.

Users of a shell may find themselves typing something similar to what they have typed before. 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. Most modern shells support command history. Shells which support command history in general also support completion from history rather than just recalling commands from the history. In addition to the plain command text, PowerShell also records execution start and end time and execution status in the command history.

Mandatory arguments/parameters are arguments/parameters which must be assigned a value upon invocation of the command, function or script file. A shell that can determine ahead of invocation that there are missing mandatory values, can assist the interactive user by prompting for those values instead of letting the command fail. Having the shell prompt for missing values will allow the author of a script, command or function to mark a parameter as mandatory instead of creating script code to either prompt for the missing values (after determining that it is being run interactively) or fail with a message. PowerShell allows commands, functions and scripts to define arguments/parameters as mandatory. The shell determines prior to invocation if there is any
mandatory arguments/parameters which have not been bound, and will then prompt the user for the value(s) before actual invocation.

Shells featuring automatic suggestions display optional command line completions as the user types. The PowerShell and fish shells natively support this feature; pressing the key inserts the completion. Implementations of this feature can differ between shells; for example, PowerShell and zsh use an external module to provide completions, and fish derives its completions from the user's command history.

Shells may record a history of directories the user has been in and allow for fast switching to any recorded location. This is referred to as a "directory stack". The concept had been realized as early as 1978 in the release of the C shell (csh). PowerShell allows multiple named stacks to be used. Locations (directories) can be pushed onto/popped from the current stack or a named stack. Any stack can become the current (default) stack. Unlike most other shells, PowerShell's location concept allow location stacks to hold file system locations as well as other location types like e. g. Active Directory organizational units/groups, SQL Server databases/tables/objects, Internet Information Server applications/sites/virtual directories. Command line interpreters 4DOS and its graphical successor Take Command Console also feature a directory stack.

A directory name can be used directly as a command which implicitly changes the current location to the directory. This must be distinguished from an unrelated load drive feature supported by Concurrent DOS, Multiuser DOS, System Manager and REAL/32, where the drive letter L: will be implicitly updated to point to the load path of a loaded application, thereby allowing applications to refer to files residing in their load directory under a standardized drive letter instead of under an absolute path.

When a command line does not match a command or arguments directly, spell checking can automatically correct common typing mistakes (such as case sensitivity, missing letters). There are two approaches to this; the shell can either suggest probable corrections upon command invocation, or this can happen earlier as part of a completion or autosuggestion. The tcsh and zsh shells feature optional spell checking/correction, upon command invocation. Fish does the autocorrection upon completion and autosuggestion. The feature is therefore not in the way when typing out the whole command and pressing enter, whereas extensive use of the tab and right arrow keys makes the shell mostly case insensitive. The PSReadLine These are not integrated features of the shells, however. PowerShell has a built in command and API functions (to be used when authoring commands) for writing/updating a progress bar. Progress bar messages are sent separates from regular command output
and the progress bar is always displayed at the ultimate interactive users console regardless of whether the progress messages originates from an interactive script, from a background job or from a remote session.

JP Software command line processors provide user configurable colorization of file and directory names in directory listings based on their file extension and/or attributes through an optionally defined environment variable. For the Unix/Linux shells, this is a feature of the command and the terminal.

The command line processors in DOS Plus, Multiuser DOS, REAL/32 and in all versions of DR DOS support a number of optional environment variables to define escape sequences allowing to control text highlighting, reversion or colorization for display or print purposes in commands like TYPE. All mentioned command line processors support %$ON% and %$OFF%. If defined, these sequences will be emitted before and after filenames. A typical sequence for would be in conjunction with ANSI. SYS, for an ASCII terminal or for an IBM or ESC/P printer. Likewise, typical sequences for would be , , , respectively. The variables %$HEADER% and %$FOOTER% are only supported by COMMAND. COM in DR DOS 7.02 and higher to define sequences emitted before and after text blocks in order to control text highlighting, pagination or other formatting options. For the Unix/Linux shells, this is a feature of the terminal.

4DOS, 4OS2, 4NT / Take Command Console and PowerShell (in PowerShell ISE) looks up context sensitive help information when is pressed. Zsh provides various forms of configurable context sensitive help as part of its widget, command, or in the completion of options for some commands. The fish shell provides brief descriptions of a command's flags during tab completion.

ShellFunctionsException handlingSearch & replace on variable substi­tutionsArith­meticFloating pointMath function libraryLinear arrays or listsAssoc­iative arraysLambda functionseval func­tionPseudo­random number generationBytecodeBourne shell 1977 versionBourne shell current versionCCP???COMMAND. COM (only Auto fail (via (or in some versions of DR DOS))OS/2 CMD. EXE? ?Windows CMD. EXE4DOS??4OS2???????? ( function)?TCC (formerly 4NT)??? ( function) (via command)PowerShell (Try Catch Finally)rc???BeanShell?? ?VMS DCLfish

ShellString processingAlternation (Brace expansion)Pattern matching (regular expressions built in)Pattern matching (filename globbing)Globbing qualifiers (filename generation based on file attributes)Recursive globbing (generating files from any level of subdirectories)Bourne shell 1977 version?Bourne shell recent version (prefix and suffix stripping in variable expansion)POSIX shell (prefix and suffix stripping in variable expansion)bash (v4.0) (prefix and suffix stripping in variable expansion) cshtcshHamilton C shellScsh? ?ksh (ksh93t+) (prefix, suffix stripping and string replacement in variable expansion) (with , no following of symlinks)pdksh?) ( or to follow symlinks)ash??CCPCOMMAND. COMOS/2 CMD. EXE (only in command)Windows CMD. EXE (only through and ) (only in command) (via command, or, where available, indirectly via subdir option)4DOS (through variable functions , extended environment variable processing, various string commands and and ) (via attribute and description options and size, time, date, and file exclusion ranges) (via command, or indirectly via command or, where available, subdir option)4OS2??? ?TCC (formerly 4NT) (through variable functions , extended environment variable processing, various string commands and and ) (via attribute and description options and size, time, date, owner, and file exclusion ranges) (via command, or indirectly via command or, where available, subdir option)PowerShellRange operator for numbers??rc??BeanShell???? ?VMS DCL (via )fish

Some operating systems define an execute permission which can be granted to users/groups for a file when the file system itself supports it. On Unix systems, the execute permission controls access to invoking the file as a program, and applies both to executables and scripts. As the permission is enforced in the program loader, no obligation is needed from the invoking program, nor the invoked program, in enforcing the execute permission this also goes for shells and other interpreter programs. The behaviour is mandated by the POSIX C library that is used for interfacing with the kernel. POSIX specifies that the exec family of functions shall fail with EACCESS (permission denied) if the file denies execution permission (see ). The execute permission only applies when the script is run directly. If a script is invoked as an argument to the interpreting shell, it will be executed regardless of whether the user holds the execute permission for that script. Although Windows also specifies an execute permission, none of the Windows specific shells block script execution if the permission has not been granted.

Several shells can be started or be configured to start in a mode where only a limited set of commands and actions is available to the user. While not a security boundary (the command accessing a resource is blocked rather than the resource) this is nevertheless typically used to restrict users' actions before logging in. A restricted mode is part of the POSIX specification for shells, and most of the Linux/Unix shells support such a mode where several of the built in commands are disabled and only external commands from a certain directory can be invoked. PowerShell supports restricted modes through session configuration files or session configurations. A session configuration file can define visible (available) cmdlets, aliases, functions, path providers and more.

Scripts that invoke other scripts can be a security risk as they can potentially execute foreign code in the context of the user who launched the initial script. Scripts will usually be designed to exclusively include scripts from known safe locations; but in some instances, e. g. when offering the user a way to configure the environment or loading localized messages, the script may need to include other scripts/files. One way to address this risk is for the shell to offer a safe subset of commands which can be executed by an included script. PowerShell data sections can contain constants and expressions using a restricted subset of operators and commands. PowerShell data sections are used when e. g. localized strings needs to be read from an external source while protecting against unwanted side effects.