使用者:LianSheng/沙盒

Bash, the default shell on many GNU/Linux systems.

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

General characteristics

Shell	Usual environment	Usually invoked	Introduced	Platform-independent	Default login shell in	Default script shell in	License	Source code availability	User interface	Mouse support	Unicode support	ISO 8601 support	Console redirection	Stream redirection	Configurability	Startup/shutdown scripts	Batch scripts	Logging	Available as statically linked, independent single file executable
Thompson shell	UNIX	sh	1971	不適用	UNIX	UNIX	不適用	是	Text-based CLI	否	否	不適用	是	不適用	不適用	不適用	不適用	不適用	不適用
Bourne shell 1977 version	7th Ed. UNIX	sh	1977	Yes	7th Ed. UNIX	7th Ed. UNIX,	Proprietary	是	Text-based CLI	否	否	不適用	是	Yes (Template:Refnec)	Yes (via variables and options)	Yes (.profile)	Yes (Unix feature)	否	是
Bourne shell current version	Various UNIX	sh	1977	Yes	SunOS-5.x, FreeBSD (non-root user)	SunOS-5.x	CDDL	是	Text-based CLI	否	是	不適用	是	Yes (Template:Refnec)	Yes (via variables and options)	Yes (.profile)	Yes (Unix feature)	是	是
POSIX shell	POSIX	sh	1992	不適用	不適用	POSIX	不適用	不適用	Text-based CLI	否	Yes, if used by configured locale	不適用	是	Yes (Template:Refnec)	Yes (via variables and options)	Unspecified (.profile given as an example)	Yes (Unix feature)	是	不適用
bash (v4)	POSIX	bash, sh	1989	是	GNU, Linux (default for root), macOS 10.3–10.14	GNU, Linux, Haiku, macOS 10.3–10.14	GPL	是	Text-based CLI	否	是	Yes (printf builtin)	是	Yes (Template:Refnec)	Yes (via variables and options)	Yes (/etc/profile, .bash_profile, .bash_login, .profile, .bashrc)	Yes (Unix feature)	是	是
csh	POSIX	csh	1978	是	SunOS	?	BSD	是	Text-based CLI	否	否	?	是	Yes (stdin, stdout, stdout+stderr)	Yes (via variables and options)	Yes (~/.cshrc, ~/.login, ~/.logout)	Yes (Unix feature)	是	是
tcsh	POSIX	tcsh, csh	1983	是	FreeBSD (default for root), formerly Mac OS X	?	BSD	是	Text-based CLI	否	是	?	是	Yes (stdin, stdout, stdout+stderr)	Yes (via variables and options)	Yes (/etc/csh.cshrc, /etc/csh.login, ~/.tcshrc, ~/.cshrc, ~/.history, ~/.login, ~/.cshdirs)	Yes (Unix feature)	是	是
Hamilton C shell	Win32, OS/2	csh	1988	是 (OS/2 version no longer maintained)	選擇性	選擇性	專有	否	Text-based CLI	否	否	Yes (-t timestamp operator)	是	Yes (stdin, stdout, stdout+stderr)	Yes (via variables and options)	Yes (via login.csh, startup.csh and logout.csh)	Yes (command line option)	是	是
Scsh	POSIX	scsh	1994	是	?	?	BSD-style	是	?	?	?	?	?	是	?	?	?	?	是
ksh (ksh93t+)	POSIX	ksh	1983	是	AIX, HP-UX	OpenSolaris	Common Public License	是	Text-based CLI	否	是	Yes (printf builtin with %(%F)T)	是	Yes (fds up to 9)	Yes (via variables and options)	Yes (system and user's profile and kshrc)	Yes (Unix feature)	是	是
pdksh	POSIX	ksh, sh	1989?	是	OpenBSD	OpenBSD	Public Domain	是	Text-based CLI	否	否	不適用	是	Yes (Template:Refnec)	Yes (via variables and options)	Yes (/etc/profile, .profile)	Yes (Unix feature)	是	是
zsh	POSIX	zsh	1990	是	Deepin, GoboLinux, Grml, macOS 10.15+	Grml, macOS 10.15+	MIT-style	是	Text-based CLI	via additional code	是	Yes (various internal features involving the date, by using the %F strftime format and the -i option for the fc builtin)	是	Yes (fds up to 9)	Yes (via variables, options, functions, styles, etc.)	Yes (system and user's zshenv, zprofile, zshrc, zlogin, zlogout)	Yes (Unix feature)	是	是
ash	POSIX	sh	1989	是	Minix, BusyBox based systems	NetBSD, Minix, BusyBox based systems	BSD-style	是	Text-based CLI	否	部份 (for BusyBox, supported in command-line editing, but not in string handling)	不適用	是	Yes (Template:Refnec)	Yes (via variables and options)	Yes (/etc/profile, .profile)	Yes (Unix feature)	是	是
CCP	CP/M, MP/M	(CCP)	1976 (1974)	否	CP/M (no login), MP/M	CP/M, MP/M	Freeware (originally proprietary)	是 (originally closed-source)	Text-based CLI	否	否	否	否	否	否	是 (automatic via $$$.SUB)	部份 (only via external SUBMIT command to update $$$.SUB)	否	是
COMMAND.COM	DOS	COMMAND	1980	否 (3rd party implementations, not bound to a specific DOS vendor or version, available)	DOS, Windows 95, 98, SE, ME	DOS, Windows 95, 98, SE, ME	vendor specific, f.e. MS-EULA, or BSD/GPL (free clones)	否 (except for OpenDOS, DR-DOS, PTS/DOS and FreeDOS)	Text-based CLI	否	否	否 (except for DR-DOS)	是 (via COMMAND con: or CTTY con:)	Yes (stdin, stdout)	是 (via startup parameters and environment variables, DR-DOS also supports DIR /C /R user-default switch command)	是 (automatic \AUTOEXEC.BAT for primary shell, or explicitly via /P, /P:filename.bat or /K startup options)	是 (via CALL command or /C and /K startup options)	否	是
OS/2 CMD.EXE	OS/2, eComStation, ArcaOS	CMD	1987	否	OS/2, eComStation, ArcaOS	OS/2, eComStation, ArcaOS	IBM-EULA	否	Text-based CLI	否	否	否	否	Yes (stdin, stdout, stderr)	?	部份 (only via /K startup option)	是 (via CALL command or /C and /K startup options)	否	是
Windows CMD.EXE	Win32	CMD	1993	否	Windows NT, 2000, XP, Server 2003, Vista	Windows NT, 2000, XP, Server 2003, Vista	MS-EULA	否	Text-based CLI	否	部份 (CHCP 65001 for UTF-8, but program arguments are still encoded in local codepage)	否	否	是	是 (via registry, startup parameters, and environment variables)	是 (automatic via registry, or explicitly via /K startup option)	是 (via CALL command or /C and /K startup options)	否	是
4DOS, NDOS	DOS, Windows 95, 98, SE, ME	4DOS, NDOS	1989 (1986)	No (not bound to a specific OS vendor or version)	選擇性	選擇性	MIT License, with restrictions	是	Text-based CLI with TUI extensions	是 (popups, help system, %_MOUSE internal variable, INKEY /M command)	否	是	是 (via CTTY con:, except for DRAWBOX, DRAWLINE, DRAWVLINE, LIST, SCREEN, SCRPUT, SELECT, VSCRPUT commands and file / directory coloring)	Yes (stdin, stdout, stderr, stdout+stderr)	是 (via 4DOS.INI/NDOS.INI file, startup parameters, environment variables, SETDOS command)	是 (automatic \AUTOEXEC.BAT for primary shell and 4START.BTM/4START.BAT as well as 4EXIT.BTM/4EXIT.BAT for any shell, or explicitly via /P, /P:dir\filename.ext or /K startup options)	是 (via CALL command or /C and /K startup options)	是	是
4OS2	OS/2, eComStation, ArcaOS	4OS2	1992	No (not bound to specific OS/2 versions)	選擇性 (but bundled with ArcaOS)	選擇性	Freeware	是	Text-based CLI	否	否	否	否	Yes (stdin, stdout, stderr, stdout+stderr)	是 (via 4OS2.INI file, startup parameters, environment variables, SETDOS command)	是 (automatic via 4START.CMD/4START.BTM as well as 4EXIT.CMD/4EXIT.BTM files, or explicitly via /K startup.cmd option)	是 (via CALL command or /C and /K startup options)	是	?
TCC (formerly 4NT)	Win32	TCC	1993	No (not bound to specific NT versions)	optional	optional	Shareware	否	Text-based CLI (Take Command: GUI)	是 (console mouse, popups, help system, %_XMOUSE, %_YMOUSE internal variables, INKEY /M command)	是	是	否	Yes (stdin, stdout, stderr, stdout+stderr)	是 (via registry, TCMD.INI/4NT.INI file, startup parameters, environment variables, SETDOS command)	是 (automatic via registry and TCSTART/4START as well as TCEXIT/4EXIT, or explicitly via /K startup option)	是 (via CALL command or /C and /K startup options)	是	否
VMS DCL	OpenVMS	Automatically for login/interactive process	1977?	是	VMS	VMS	Proprietary, bundled in VMS	by special license only	Text-based CLI	with DECwindows/Motif	是	Yes, at least to 1988 standard	是	Yes (sys$input, sys$output assignment)	Yes (via symbols, logical names, and options)	Yes (SYS$MANAGER:SYLOGIN.COM and user defined LOGIN.COM)	是	是	否
PowerShell	.NET, .NET Framework	PowerShell	2006	是	Windows 10, 8, Server 2008, 7	Windows 10, 8, Server 2008, 7	MIT-style	是	Graphical CLI	是	是	是	是	是	Yes (via variables and options)	Yes (%USERPROFILE%\Documents \WindowsPowerShell\Microsoft.PowerShell_profile.ps1)	Yes (PowerShell feature)	是	否
rc	Plan 9, POSIX	rc	1989	是	Plan 9, Version 10 Unix	Plan 9, Version 10 Unix	MIT License	?	?	?	是	?	?	是	?	?	?	?	是
BeanShell	Java	?	2005	是	?	?	LGPL	?	?	?	是	?	?	是	?	?	?	?	否
fish	POSIX	fish	2005	是	GhostBSD	?	GPL	是	Text-based CLI	?	是	?	?	Yes (Template:Refnec)	Yes (through environment variables and via web interface through fish_config)	Yes (/etc/fish/config.fish and ~/.config/fish/config.fish)	Yes (Unix feature)	Yes (~/.config/fish/fish_history*)	?
Ion	Redox, Linux	ion	2015	是	Redox	Redox	MIT	是	Text-based CLI	?	是	是	?	Yes (Template:Refnec)	Yes (follows the XDG Base Directory spec)	Yes (~/.config/ion/initrc)	Yes	Yes (~/.local/share/ion/history)	部份 (not distributed as a standalone executable, but it can be built as one)
Shell	Usual environment	Usually invoked	Introduced	Platform-independent	Default login shell in	Default script shell in	License	Source code availability	User interface	Mouse support	Unicode support	ISO 8601 support	Console redirection	Stream redirection	Configurability	Startup/shutdown scripts	Batch scripts	Logging	Available as statically linked, independent single file executable

Interactive features

Shell	Command name completion	Path completion	Command argument completion	Wildcard completion	Command history	Mandatory argument prompt	Automatic suggestions	Colored directory listings	Text highlighting	Syntax highlighting	Directory history, stack or similar features	Implicit directory change	Auto­correction	Integrated environment	Snippets	Value prompt	Menu/options prompt	Progress indicator	Context sensitive help	Command builder
Thompson shell	否	否	否	否	否	否	否	?	?	否	否	否	否	否	否	否	否	否	否	否
Bourne shell 1977 version	否	否	否	否	否	否	否	?	?	否	否	否	否	否	否	是	否	External	否	否
Bourne shell current version	否	是	否	否	是	否	否	是	是	否	是 (CDPATH, pushd, popd, dirs), CDPATH since SVr4	否	否	否	否	是	否	External	否	否
POSIX shell	否	否	否	否	是	否	否	是	是	否	Yes (CDPATH)	否	否	否	否	是	否	External	否	否
bash (v4.0)	是	是	when defined	是	是	否	否	是	是	否	Yes (CDPATH, pushd, popd)	optional	否	否	否	是	是	External	否	否
csh	是	是	否	否	是	否	否	是	是	否	Yes (cdpath, pushd, popd)	optional	否	否	否	是	否	External	否	否
tcsh	是	是	when defined	否	是	否	否	是	是	否	Yes (cdpath, pushd, popd)	optional	是	否	否	是	否	External	否	否
Hamilton C shell	是	是	否	是	是	否	否	是	是	否	Yes (cdpath, pushd, popd)	否	否	否	否	是	否	External	否	否
Scsh	否	否	否	否	否	否	否	?	?	否	否	否	否	否	否	是	否	External	否	否
ksh (ksh93t+)	Yes (extendable)	Yes (extendable)	否	否	是	否	否	是	是	否	Yes (cdpath builtin, pushd, popd implemented as functions)	否	否	否	否	是	是	External	否	否
pdksh	是	是	否	否	是	否	否	是	是	否	否	否	否	否	否	是	是	External	否	否
zsh	是	是	when defined	是	是	是	Yes (via predict-on or user-defined)	是	是	Third-party extension	是	optional	是	否	when defined (as ZLE widgets)	是	是	External	是	否
ash	否	否	否	否	是	否	否	是	是	否	否	否	否	否	否	是	是	External	否	否
CCP	否	否	否	否	否	否	否	否	否	否	否	否	否	否	否	否	否	否	否	否
COMMAND.COM	否	否	否	否	否	否	否	否	否 (only in DR-DOS through %$ON%, %$OFF%, %$HEADER%, %$FOOTER%)	否	否	否	否	否 (only single-stepping with COMMAND /Y)	否	否	否 (only via external CHOICE command, in DR-DOS also via SWITCH / DRSWITCH internal commands)	否	否	否
OS/2 CMD.EXE	是	是	否	否	是	否	否	否	否	否	否	否	否	否	否	否	否	否	否	否
Windows CMD.EXE	partial	partial	否	否	Yes (F8)	否	否	否	否	否	Yes (PUSHD, POPD)	否	否	否	否	是 (via SET /P command)	否	否	否	否
4DOS	是	是	是	是	是	否	否	是	否	否	(via popup, extended directory searches, CDPATH, PUSHD, POPD, DIRHISTORY, DIRS, CDD, CD - commands and %@DIRSTACK[] function)	是	否	是	否	是 (via INPUT, INKEY and ESET commands)	是 (via @SELECT[] function, and indirectly via a combination of INKEY, INPUT, SWITCH commands)	否	是	否 (except for OPTION command for INI file directives)
4OS2	?	?	?	?	是	否	否	是	否	否	是	是	否	?	否	?	?	否	是	否
TCC (formerly 4NT)	是	是	是	是	是	否	否	是	否	是	(via popup, extended directory searches, CDPATH, PUSHD, POPD, DIRHISTORY, DIRS, CDD, CD - commands and %@DIRSTACK[] function)	是	否	是	否	是 (via INPUT, INKEY, ESET and SET /P commands)	是 (via @SELECT[] function, and indirectly via a combination of INKEY, INPUT, SWITCH commands)	否	是	否
PowerShell	是	是	是	是	Yes (F8)	是	Yes; via PSReadLine module (bundled in v5.0) or in ISE	Third-party extension	是	Yes; via PSReadLine module (bundled in v5.0) or in ISE	Yes (multiple stacks; multiple location types; Push-Location, Pop-Location)	Yes, in PSReadLine module	Yes, in ISE	Yes, in ISE	是	是	是	是, in ISE	popup window	是, in ISE
rc	是	是	否	否	是	否	否	?	?	否	否	否	否	否	否	?	否	否	否	否
BeanShell	是	是	否	否	否	否	否	?	?	否	否	否	否	否	否	否	否	否	否	否
VMS DCL	Minimum uniqueness scheme	否	否	否	是	是	否	?	?	否	否	否	否	否	否	是	否	否	否	否
fish	是	是	when defined or parsable in man pages	是	是	否	是	是	Yes (built-in helper available)	是	是	是	是	是	Yes, using abbr command	是	(via fish_config command)	否	否	否
Shell	Command name completion	Path completion	Command argument completion	Wildcard completion	Command history	Mandatory argument prompt	Automatic suggestions	Colored directory listings	Text highlighting	Syntax highlighting	Directory history, stack or similar features	Implicit directory change	Auto­correction	Integrated environment	Snippets	Value prompt	Menu/options prompt	Progress indicator	Context sensitive help	Command builder

Background execution

Background execution allows a shell to run a command in background. POSIX shells and other Unix shells allow background execution by using the & character at the end of command, and in PowerShell you can use Start-Process or Start-Job commands.

Completions

主條目：Command-line completion

Command-line completion in Bash.

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 Tab ↹ 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.

Command history

主條目：Command history

A user of a shell may find that he/she is typing something similar to what the user typed before. If the shell supports command history the user can call the previous command into the line editor and edit it before issuing it again.

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 argument prompt

更多資訊：Named parameter § Optional parameters

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.

Automatic suggestions

主條目：Autocomplete

Command-line completion in PowerShell.

Shells featuring automatic suggestions display optional command-line completions as the user types. The PowerShell and fish shells natively support this feature; pressing the Tab ↹ 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.

Directory history, stack or similar features

更多資訊：pushd and popd

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.

Implicit directory change

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.

Autocorrection

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 PowerShell module (which is shipped with version 5.0) provides the option to specify a CommandValidationHandler ScriptBlock which runs before submitting the command. This allows for custom correcting of commonly mistyped commands, and verification before actually running the command.

Progress indicator

A shell script (or job) can report progress of long running tasks to the interactive user.

Unix/Linux systems may offer other tools support using progress indicators from scripts or as standalone-commands, such as the program "pv". 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.

Interactive table

Output from a command execution can be displayed in a table/grid which can be interactively sorted and filtered and/or otherwise manipulated after command execution ends.

PowerShell Out-GridView cmdlet displays data in an interactive window with interactive sorting and filtering.

Colored directory listings

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 %COLORDIR% environment variable.

For the Unix/Linux shells, this is a feature of the ls command and the terminal.

Text highlighting

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 %$ON% would be \033[1m in conjunction with ANSI.SYS, \033p for an ASCII terminal or \016 for an IBM or ESC/P printer. Likewise, typical sequences for %$OFF% would be \033[0m, \033q, \024, 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.

Syntax highlighting

主條目：Syntax highlighting

An independent project offers syntax highlighting as an add-on to the Z Shell (zsh). This is not part of the shell, however.

PowerShell provides customizable syntax highlighting on the command line through the PSReadLine module. This module can be used with PowerShell v3.0+, and it's included with v5.0. Additionally, it is loaded by default in the command line host "powershell.exe" in v5.0. The PowerShell ISE also includes syntax highlighting on the command line as well as in the script pane. Take Command Console (TCC) offers syntax highlighting in the integrated environment.

Context sensitive help

主條目：Context-sensitive help

4DOS, 4OS2, 4NT / Take Command Console and PowerShell (in PowerShell ISE) looks up context-sensitive help information when F1 is pressed.

Zsh provides various forms of configurable context-sensitive help as part of its run-help widget, _complete_help command, or in the completion of options for some commands.

Command builder

A command builder is a guided dialog which assists the user in filling in a command. PowerShell has a command builder which is available in PowerShell ISE or which can be displayed separately through the Show-Command cmdlet.

Programming features

Shell	Functions	Exception handling	Search & replace on variable substi­tutions	Arith­metic	Floating point	Math function library	Linear arrays or lists	Assoc­iative arrays	Lambda functions	eval func­tion	Pseudo­random number generation	Bytecode
Bourne shell 1977 version	否	Yes (via trap)	否	否	否	否	否	否	否	是	否	否
Bourne shell current version	Yes since SVR2	Yes (via trap)	否	是	否	否	否	否	否	是	否	否
POSIX shell	是	Yes (via trap)	否	是	否	否	否	否	否	是	否	否
bash (v4.0)	是	Yes (via trap)	Yes (via ${//} syntax)	是	否	否	是	是	否	是	Yes ($RANDOM)	否
csh	否	否	Yes (via $var:s/// syntax)	是	否	否	是	否	否	是	否	否
tcsh	否	否	Yes (via $var:s/// syntax)	是	否	否	是	否	否	是	否	否
Hamilton C shell	是	否	Yes (via $var:s/// syntax)	是	是	是	是	否	否	是	Yes (random utility)	否
Scsh	是	?	Yes (via string functions and regular expressions)	?	?	?	是	?	是	是	Yes (random-integer, random-real)	Yes (compiler is Scheme48 virtual machine, via scshvm)
ksh (ksh93t+)	是	Yes (via trap)	Yes (via ${//} syntax and builtin commands)	是	是	是	是	是	否	是	Yes ($RANDOM)	Yes (compiler is called shcomp)
pdksh	是	Yes (via trap)	否	是	否	否	是	否	否	是	Yes ($RANDOM)	否
zsh	是	是	Yes (via ${:s//} and ${//} syntax)	是	是	Yes (zsh/mathfunc module)	是	是	否	是	Yes ($RANDOM)	Yes (built-in zcompile command)
ash	是	是 (via trap)	否	Yes (since 1992)	否	否	否	否	否	是	否	否
CCP	否	?	否	否	?	?	否	否	否	否	否	否
COMMAND.COM	否	部份 (only Auto-fail (via COMMAND /F (or /N in some versions of DR-DOS))	否	否	否	否	否	否	否	否	否	否
OS/2 CMD.EXE	否	否	否	?	否	否	?	否	否	否	否	否
Windows CMD.EXE	Yes (via CALL :label)	否	Yes (via SET %varname:expression syntax)	Yes (via SET /A)	否	否	Yes (via SET)	否	否	否	Yes (%random%)	否
4DOS	是	Yes (via ON command, optional Auto-fail via 4DOS /F)	Yes (via %@Replace[...] function)	Yes (via SET /A)	?	?	Yes (via ranges, include lists, @file lists and FOR command)	否	否	是	Yes (%@Random[...] function)	Yes (via BATCOMP command)
4OS2	?	?	?	?	?	?	?	?	否	是	是 (%@Random[...] function)	?
TCC (formerly 4NT)	是	Yes (via ON and various ...MONITOR commands)	Yes (via %@Replace[...] function)	Yes (via SET /A)	?	?	Yes (via ranges, include lists, @file lists and FOR command)	?	否	是	是 (%@Random[...] function)	是 (via BATCOMP command)
PowerShell	是	是 (Try-Catch-Finally)	Yes (-replace operator)	是	是	[Math] class	是	是	是	是	是	Yes, automatic
rc	是	是	否	?	?	?	是	?	否	是	否	否
BeanShell	是	是	?	是	?	?	是	是	否	是	是	是
VMS DCL	是	是	否	是	否	yes, for compiled programs	是	否	否	否	否	否
fish	是	Yes (via trap)	Yes, via string builtin command	是	是	是	是	否	否	是	Yes (random)	否

String processing and filename matching

Shell	String processing	Alternation (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	?	否	否	Yes (*, ?, [...])	否	否
Bourne shell recent version	部份 (prefix and suffix stripping in variable expansion)	否	否	Yes (*, ?, [...])	否	否
POSIX shell	部份 (prefix and suffix stripping in variable expansion)	否	否	Yes (*, ?, [...])	否	否
bash (v4.0)	部份 (prefix and suffix stripping in variable expansion)	是	是	Yes (*, ?, [...], {...})	否	是 (**/...)
csh	Yes (:s and other editing operators)	是	否	是	否	否
tcsh	Yes (:s and other editing operators)	是	是	是	否	否
Hamilton C shell	Yes (:s and other editing operators + substr, strlen, strindex, printf, reverse, upper, lower, concat and other builtin functions)	是	否	是	否	Yes (via indefinite directory "..." wildcard)
Scsh	?	?	是	是	否	否
ksh (ksh93t+)	部份 (prefix, suffix stripping and string replacement in variable expansion)	是	是	Yes (*, ?, [...])	否	是 (with set -G, no following of symlinks)
pdksh	?	是	否	是	否	否
zsh	是 (through variable processing: e.g. substring extraction, various transformations via parameter expansion)	是	是	Yes (*, ?, [...], extended globbing)	是	是 (**/... or ***/... to follow symlinks)
ash	?	?	否	是	否	否
CCP	否	否	否	否	否	否
COMMAND.COM	否	否	否	Yes (*, ?)	否	否
OS/2 CMD.EXE	否	否	否	Yes (*, ?)	部份 (only in DIR /A:... command)	否
Windows CMD.EXE	部份 (only through FOR /F and SET /A)	否	No	Yes (*, ?)	部份 (only in DIR /A:... command)	是 (via FOR /R command, or, where available, indirectly via /S subdir option)
4DOS	是 (through variable functions %@...[], extended environment variable processing, various string commands and FOR /F and SET /A)	否	否	Yes (*, ?, [...], extended wildcards, SELECT popup command)	是 (via /A:... attribute and /I"..." description options and /[S...] size, /[T...] time, /[D...] date, and /[!...] file exclusion ranges)	是 (via FOR /R command, or indirectly via GLOBAL command or, where available, /S subdir option)
4OS2	?	否	否	?	?	?
TCC (formerly 4NT)	是 (through variable functions %@...[], extended environment variable processing, various string commands and FOR /F and SET /A)	否	是	Yes (*, ?, [...], extended wildcards, SELECT popup command)	是 (via /A:... attribute and /I"..." description options and /[S...] size, /[T...] time, /[D...] date, /[O...] owner, and /[!...] file exclusion ranges)	是 (via FOR /R command, or indirectly via GLOBAL command or, where available, /S subdir option)
PowerShell	Yes (Concat/Substring/Insert/Remove/Replace, ToLower/ToUpper, Trim/TrimStart/TrimEnd, Compare, Contains/StartsWith/EndWith, Format, IndexOf/LastIndexOf, Pad/PadLeft/PadRight, Split/Join, regular expression functions and other .NET string functions)	Range operator for numbers	Yes (full regex support)	Yes (*, ?, [...])	?	?
rc	?	?	否	是	否	否
BeanShell	?	?	是	?	?	?
VMS DCL	是	否	否	是	否	是 (via [SUBDIR...])
fish	Yes (builtin string function)	Yes	yes (via builtin string match and string replace functions)	Yes (*, ?, {...})	否	是 (**/...)

Inter-process communication

Shell	Pipes	Command substitution	Process substitution	Subshells	TCP/UDP connections as streams	Keystroke stacking
Bourne shell	bytes concurrent	是	否	是	否	不適用
POSIX shell	bytes concurrent	是	否	是	否	不適用
bash (v4.0)	bytes concurrent	是	Yes (if system supports /dev/fd/⟨n⟩ or named pipes)	是	Yes (client only)	不適用
csh	bytes concurrent	是	否	是	否	不適用
tcsh	bytes concurrent	是	否	是	否	不適用
Hamilton C shell	bytes concurrent	是	否	是	否	?
Scsh	text	?	?	?	是	不適用
ksh (ksh93t+)	bytes (may contain serialized objects if print -C is used) concurrent	Yes ($(...) and ${<space>...;})	Yes (if system supports /dev/fd/⟨n⟩)	是	Yes (and SCTP support, client only)	不適用
pdksh	bytes concurrent	是	否	是	否	不適用
zsh	bytes concurrent	是	是	是	Yes (client and server, but only TCP)	不適用
ash	bytes concurrent	是	否	是	否	不適用
CCP	否	否	否	否	否	否
COMMAND.COM	text sequential temporary files	否	否	部份 (only under DR-DOS multitasker via COMMAND.COM /T)	否	否
OS/2 CMD.EXE	text concurrent	否	否	?	否	否
Windows CMD.EXE	text concurrent	Yes (via FOR /F command)	否	Yes (Backtick: ` in FOR /F usebackq)	否	否
4DOS	text sequential temporary files	Yes (via FOR /F command)	?	部份 (via %@EXECSTR[] and %@EXEC[], or via SET /M, ESET /M and UNSET /M and %@MASTER[...])	否	是 (via KEYSTACK and KSTACK)
4OS2	text concurrent	?	?	?	否	是 (via KEYSTACK)
TCC (formerly 4NT)	text concurrent	Yes (via FOR /F command)	?	部份 (via %@EXECSTR[] and %@EXEC[])	是 (via FTP, TFTP, FTPS, SFTP, HTTP, HTTPS and IFTP, client only)	是 (via KEYSTACK)
PowerShell	objects concurrent	是	否	是	是	?
rc	text concurrent	是	Yes (via: <{cmd} if system supports /dev/fd/⟨n⟩)	是	否	?
BeanShell	not supported	?	?	?	是	?
VMS DCL	text (via PIPE command)	是	否	Yes (spawn)	Yes (server TCP only)	否
fish	bytes concurrent	是 (...)	No (broken)	否	否	不適用

Keystroke stacking

In anticipation of what a given running application may accept as keyboard input, the user of the shell instructs the shell to generate a sequence of simulated keystrokes, which the application will interpret as a keyboard input from an interactive user. By sending keystroke sequences the user may be able to direct the application to perform actions that would be impossible to achieve through input redirection or would otherwise require an interactive user. For example, if an application acts on keystrokes, which cannot be redirected, distinguishes between normal and extended keys, flushes the queue before accepting new input on startup or under certain conditions, or because it does not read through standard input at all. Keystroke stacking typically also provides means to control the timing of simulated keys being sent or to delay new keys until the queue was flushed etc. It also allows to simulate keys which are not present on a keyboard (because the corresponding keys do not physically exist or because a different keyboard layout is being used) and therefore would be impossible to type by a user.

Security features

Shell	Secure (password) prompt	Encrypted variables/ parameters	File/directory passwords	Execute permission	Untrusted script blocking	Restricted shell subset	Safe data subset
Bourne shell	via stty	否	?	不適用	否	是	否
POSIX shell	via stty	否	?	不適用	否	否	否
bash (v4.0)	read -s	否	?	不適用	否	是	否
csh	via stty	否	?	不適用	否	是	否
tcsh	via stty	否	?	不適用	否	是	否
Hamilton C shell	否	否	否	否	否	否	否
Scsh	via stty	否	?	不適用	否	否	否
ksh (ksh93t+)	via stty	否	?	不適用	否	是	否
pdksh	via stty	否	?	不適用	否	是	否
zsh	read -s	否	?	不適用	否	是	否
ash	via stty	否	?	不適用	否	是	否
CCP	否	否	否	否	否	否	否
COMMAND.COM	部份 (only under DR-DOS, prompts for password if file/directory is protected)	否	部份 (only under DR-DOS via \dirname;dirpwd\filename;filepwd syntax)	部份 (only under DR-DOS, if files are password-protected for read and/or execute permission)	否	否	否
OS/2 CMD.EXE	否	否	否	否	否	否	否
Windows CMD.EXE	否	否	否	否	否	否	否
4DOS	是 (via INPUT /P or INKEY /P)	否	部份 (only under DR-DOS via \dirname;;dirpwd\filename;;filepwd syntax)	部份 (only under DR-DOS, if files are password-protected for read and/or execute permission)	否	否	否
4OS2	?	否	否	否	否	否	否
TCC (formerly 4NT)	是 (via INPUT /P, INKEY /P or QUERYBOX /P)	否	否	否	否	否	否
PowerShell	是	是	否	否	是	是	是
rc	via stty	否	?	不適用	否	是	否
BeanShell	?	?	?	?	?	?	?
VMS DCL	是	否	否	是	否	是	否
fish	read -s	否	?	不適用	否	Yes (via fish -l)	?

Secure prompt

Some shell scripts need to query the user for sensitive information such as passwords, private digital keys, PIN codes or other confidential information. Sensitive input should not be echoed back to the screen/input device where it could be gleaned by unauthorized persons. Plaintext memory representation of sensitive information should also be avoided as it could allow the information to be compromised, e.g., through swap files, core dumps etc.

The shells bash, zsh and PowerShell offer this as a specific feature. Shells which do not offer this as a specific feature may still be able to turn off echoing through some other means. Shells executing on a Unix/Linux operating system can use the stty external command to switch off/on echoing of input characters. In addition to not echoing back the characters, PowerShell's -AsSecureString option also encrypts the input character-by-character during the input process, ensuring that the string is never represented unencrypted in memory where it could be compromised through memory dumps, scanning, transcription etc.

Encrypted variables/parameters

If a script reads a password into an environment variable it is in memory in plain text, and thus may be accessed via a core dump. It is also in the process environment, which may be accessible by other processes started by the script.

PowerShell can work with encrypted string variables/parameters. Encrypted variables ensure that values are not inadvertently disclosed through e.g. transcripts, echo'ing, logfiles, memory or crash dumps or even malicious memory scanning. PowerShell also supports saving of such encrypted strings in text files, protected by a key owned by the current user.

Execute permission

Some operating systems define an execute permission which can be granted to users/groups for a file.

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 execve – 系統界面（System Interfaces）參考，單一UNIX®規範第7期，由國際開放標準組織發布).

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.

Untrusted script blocking

Some shells will block scripts determined to be untrustworthy, or refuse to run scripts if mandated by a system administrator.

Script origin execution restriction

PowerShell can be set to block execution of scripts which has been marked as obtained from an unknown/untrusted origin (e.g. the Internet). Internet facing applications such as web browsers, IM clients, mail readers etc. mark files downloaded from the internet with the origin zone in an alternate data stream which is understood by PowerShell.

Signed script restriction

Script/code signing policies can be used to ensure that an operations department only run approved scripts/code which have been reviewed and signed by a trusted reviewer/approver. Signing regimes also protects against tampering. If a script is sent from vendor to a client, the client can use signing to ensure that the script has not been tampered with during transit and that the script indeed originates from the vendor and not an attacker trying to social engineer an operator into running an attack script.

PowerShell can be set to allow execution of otherwise blocked scripts (e.g. originating from an untrusted zone) if the script has been digitally signed using a trusted digital certificate.

Multilevel execution policies

A company may want to enforce execution restriction globally within the company and/or certain parts of the company. It may want to set a policy for running signed scripts but allow certain parts of the company to set their own policies for zoned restrictions.

PowerShell allows script blocking policies to be enforced at multiple levels: Local machine, current user etc. A higher level policy overrides a lower level policy, e.g. if a policy is defined for the local machine it is in place for all users of the local machine, only if it is left undefined at the higher level can it be defined for the lower levels.

Restricted shell subset

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.

Safe data subset

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.

External links

• Nasarek, Marcus. Article (PDF). Comparing Bash with the Windows Vista shell: Shell Games. Linux Magazine. May 2007. （原始內容存檔 (PDF)於Oct 10, 2014）. 
• Base Specifications - Shell and Utilities. IEEE 1003.1 Standard for Information Technology – Portable Operating System Interface (POSIX) 2018. Open Group. 2017.