Difference between sh and Bash

Question

When writing shell programs, we often use /bin/sh and /bin/bash. I usually use bash, but I don't know what's the difference between them.

What's main difference between Bash and sh?

What do we need to be aware of when programming in Bash and sh?

Povertystricken

For a useful list of bashisms and corresponding code that works on Bourne shell, see mywiki.wooledge.org/Bashism – Joanne

You may want to see the POSIX standard for sh and its command language: * sh * Shell Command Language – Droppings

as a general rule, all sh scripts will run under bash thanks to it's posix compatibility, but not all bash scripts can run under sh, the main differences you notice are things like [[ ]] instead of [ ] comparisons which allow unquoted spaces, $(( )) instead of $[ ] arithmetic expressions, and other things like "its too big and too slow" directly from the bash docs.. But new scripters need not limit themselves to sh-compatible scripts unless they are shooting for some backward compatibility, which more often than not is not the case these days, after all it is (or was...) the year 2014 right?? – Inaugurate

<<But new scripters need not limit themselves to sh-compatible scripts unless they are shooting for some backward compatibility>> backward presumes one dimension in which linux is the only thing still growing. i use linux but also bsd, and i won't install bash unless i need it. so, i limit my shell scripting to the posix-level bourne shell, which is fairly modern, having functions and local variables and so on. portability has more than one dimension, it's not just backward/forward. – Sexuality

If you are forced to switch from bash to POSIX, you will most of all stumble over what is missing: No arrays, no builtin line editing (though you possibly can get this using rlwrap or by running a reasonable shell such as bash or zsh in "posix mode"), less globing facilities and so on. Enough that you will start swearing sooner or later. If in doubt of what still works, have a look here – Perpetual

Answer 1

What is sh?

sh (or the Shell Command Language) is a programming language described by the POSIX standard. It has many implementations (ksh88, Dash, ...). Bash can also be considered an implementation of sh (see below).

Because sh is a specification, not an implementation, /bin/sh is a symlink (or a hard link) to an actual implementation on most POSIX systems.

What is Bash?

Bash started as an sh-compatible implementation (although it predates the POSIX standard by a few years), but as time passed it has acquired many extensions. Many of these extensions may change the behavior of valid POSIX shell scripts, so by itself Bash is not a valid POSIX shell. Rather, it is a dialect of the POSIX shell language.

Bash supports a --posix switch, which makes it more POSIX-compliant. It also tries to mimic POSIX if invoked as sh.

sh = bash?

For a long time, /bin/sh used to point to /bin/bash on most GNU/Linux systems. As a result, it had almost become safe to ignore the difference between the two. But that started to change recently.

Some popular examples of systems where /bin/sh does not point to /bin/bash (and on some of which /bin/bash may not even exist) are:

1. Modern Debian and Ubuntu systems, which symlink sh to dash by default;
2. Busybox, which is usually run during the Linux system boot time as part of initramfs. It uses the ash shell implementation.
3. BSD systems, and in general any non-Linux systems. OpenBSD uses pdksh, a descendant of the KornShell. FreeBSD's sh is a descendant of the original Unix Bourne shell. Solaris has its own sh which for a long time was not POSIX-compliant; a free implementation is available from the Heirloom project.

How can you find out what /bin/sh points to on your system?

The complication is that /bin/sh could be a symbolic link or a hard link. If it's a symbolic link, a portable way to resolve it is:

% file -h /bin/sh
/bin/sh: symbolic link to bash

If it's a hard link, try

% find -L /bin -samefile /bin/sh
/bin/sh
/bin/bash

In fact, the -L flag covers both symlinks and hardlinks, but the disadvantage of this method is that it is not portable — POSIX does not require find to support the -samefile option, although both GNU find and FreeBSD find support it.

Shebang line

Ultimately, it's up to you to decide which one to use, by writing the «shebang» line as the very first line of the script.

E.g.

#!/bin/sh

will use sh (and whatever that happens to point to),

#!/bin/bash

will use /bin/bash if it's available (and fail with an error message if it's not). Of course, you can also specify another implementation, e.g.

#!/bin/dash

Which one to use

For my own scripts, I prefer sh for the following reasons:

• it is standardized
• it is much simpler and easier to learn
• it is portable across POSIX systems — even if they happen not to have bash, they are required to have sh

There are advantages to using bash as well. Its features make programming more convenient and similar to programming in other modern programming languages. These include things like scoped local variables and arrays. Plain sh is a very minimalistic programming language.

Ronn

If you run a script with bash the display way more useful error messages in the case of syntax error. You can simply save time by using bash. – Petitioner

What does the % mean at the beginning of your command lines? – Taxeme

@JosephHarriott it's a prompt: a character printed by the shell itself after which your command follows. Some shells use $ instead of %, or # for the root shell. – Ronn

@RomanCheplyaka which shells ? I've only ever seen $ and #... – Taxeme

@RomanCheplyaka I am certain sh existed well before bash (which stands for bourne-again shell). But it was very primitive and didn't respond to terminal events, like ESC characters. Then ksh came (also before bash), then bash started by those who loved the idea of a better shell, but hated ksh. :-) – Prod

@JosephHarriott - % is commonly the prompt for user shells of the C Shell variety (e.g. csh, tcsh). # has been traditionally reserved as the prompt character for superuser (root) shells, regardless of which one is chosen. But that's all in the realm of common / typical usage, as historically / traditionally observed. You can use what you like and/or what your users will tolerate. :) Google on how – Savagism

You say you prefer sh . What is the documentation for sh? Everything I find is with BASH? So what a mess. Also, what is the problem if in a script that I have bash #!/bin/bash I do sh script_with_bash.sh , I see the same thing happens. – Discomfiture

The default prompt in Zsh is also %, even though traditionally that was used to signify a Csh-family shell. This is by no means the only area where Zsh deviates from tradition. – Palpebrate

It would be nice if you could add info about macOS in your answer too. Btw, why do we have to point to the current directory ./ to run a script when you are already there? – Hormonal

@Roberto, when calling an executable (any file with the executable bit set) without a path, such as script, the shell looks for it in the PATH env var (this is a set of directories to search for executables in). The shell skips the PATH lookup for absolute or relative executable paths, such as ./script, /abs/path/script, or rel/path/script. Therefore, if your working directory is not in the PATH, then trying to execute script won't work because it can't be found, assuming the script name can't be found on the PATH. – Foliose

Answer 2

sh: http://man.cx/sh
Bash: http://man.cx/bash

TL;DR: Bash is a superset of sh with a more elegant syntax and more functionality. It is safe to use a Bash shebang line in almost all cases as it's quite ubiquitous on modern platforms.

NB: in some environments, sh is Bash. Check sh --version.

Neel

if bash is invoked as sh, it behaves a bit differently. See gnu.org/software/bash/manual/bashref.html#Bash-Startup-Files ("Invoked with name sh") and gnu.org/software/bash/manual/bashref.html#Bash-POSIX-Mode. For example, no process substitution. – Basswood

As bash is a superset of sh and some OS like FreeBSD do not have bash installed by default, scripting in sh will give greater portability. – Heteromorphic

As there is no portable scriptable way to get a POSIX shell for a specific script, portable scripts cannot assume more than Bourne Shell features. – Maximilien

...eh, if someone doesn't put a POSIX-compliant sh in the PATH before the first noncompliant one, that's their fault and they deserve what they get; #!/usr/bin/env sh and blaming-the-user comes close enough for practical purposes. :) – Geyer

On Git Bash for Windows, sh runs bash in POSIX mode (gnu.org/software/bash/manual/html_node/…) – Selfcentered

Answer 3

This question has frequently been nominated as a canonical for people who try to use sh and are surprised that it's not behaving the same as bash. Here's a quick rundown of common misunderstandings and pitfalls.

First off, you should understand what to expect.

• If you run your script with sh scriptname, or run it with scriptname and have #!/bin/sh in the shebang line, you should expect POSIX sh behavior.
• If you run your script with bash scriptname, or run it with scriptname and have #!/bin/bash (or the local equivalent) in the shebang line, you should expect Bash behavior.

Having a correct shebang and running the script by typing just the script name (possibly with a relative or full path) is generally the preferred solution. In addition to a correct shebang, this requires the script file to have execute permission (chmod a+x scriptname).

So, how do they actually differ?

Bash aims to be backwards-compatible with the Bourne shell and POSIX, but has many additional features. The Bash Reference manual has a section which attempts to enumerate the differences but some common sources of confusion include

• [[ is not available in sh (only [ which is more clunky and limited). See also Difference between single and double square brackets in Bash
• sh does not have arrays.
• Some Bash keywords like local, source, function, shopt, let, declare, and select are not portable to sh. (Some sh implementations support e.g. local.)
• Bash has many C-style syntax extensions like the three-argument for((i=0;i<=3;i++)) loop, += increment assignment, etc. The $'string\nwith\tC\aescapes' feature is tentatively accepted for POSIX (meaning it works in Bash now, but will not yet be supported by sh on systems which only adhere to the current POSIX specification, and likely will not for some time to come).
• Bash supports <<<'here strings'.
• Bash has *.{png,jpg} and {0..12} brace expansion.
• Bash has extended globbing facilities like ** (globstar) for recursing subdirectories, and extglob for using a different, more versatile wildcard syntax.
• ~ refers to $HOME only in Bash (and more generally ~username to the home directory of username).This is in POSIX, but may be missing from some pre-POSIX /bin/sh implementations.
• Bash has process substitution with <(cmd) and >(cmd).
• Bash has Csh-style convenience redirection aliases like &| for 2>&1 | and &> for > ... 2>&1
• Bash supports coprocesses with <> redirection.
• Bash features a rich set of expanded non-standard parameter expansions such as ${substring:1:2}, ${variable/pattern/replacement}, case conversion, etc.
• Bash has significantly extended facilities for shell arithmetic (though still no floating-point support). There is an obsolescent legacy $[expression] syntax which however should be replaced with POSIX arithmetic $((expression)) syntax. (Some legacy pre-POSIX sh implementations may not support that, though.)
• Several built-in commands have options which are not portable, like type -a, printf -v, and the perennial echo -e.
• Magic variables like $RANDOM, $_, $SECONDS, $PIPESTATUS[@] and $FUNCNAME are Bash extensions. See the Reference Manual.
• Bash exposes some system facilities as file handles, like /dev/stdin, /dev/fd/<number>, /dev/tcp/<network address>, etc
• Syntactic differences like export variable=value and [ "x" == "y" ] which are not portable (export variable should be separate from variable assignment, and portable string comparison in [ ... ] uses a single equals sign).
• Many, many Bash-only extensions to enable or disable optional behavior and expose internal state of the shell.
• Many, many convenience features for interactive use which however do not affect script behavior.

Remember, this is an abridged listing. Refer to the reference manual for the full scoop, and http://mywiki.wooledge.org/Bashism for many good workarounds; and/or try http://shellcheck.net/ which warns for many Bash-only features.

A common error is to have a #!/bin/bash shebang line, but then nevertheless using sh scriptname to actually run the script. This basically disables any Bash-only functionality, so you get syntax errors e.g. for trying to use arrays. (The shebang line is syntactically a comment, so it is simply ignored in this scenario.)

Unfortunately, Bash will not warn when you try to use these constructs when it is invoked as sh. It doesn't completely disable all Bash-only functionality, either, so running Bash by invoking it as sh is not a good way to check if your script is properly portable to ash/dash/POSIX sh or variants like Heirloom sh. If you want to check for strict POSIX compliance, try posh in its designated POSIX mode (which however does not seem to be properly documented).

As an aside, the POSIX standardization effort is intended to specify the behavior of various U*x-like platform behaviors, including the shell (sh). However, this is an evolving document, and so, some implementations adhere to an earlier version of the POSIX specification; furthermore, there are some legacy implementations which didn't even try to adhere to POSIX. The original Bourne shell had some quirks which were later straightened out by the POSIX spec, which in large parts is based on ksh88. (Many of the Bash extensions are also innovations from ksh.)

Palpebrate

Fundamentally, the TL;DR ersion is And's answer. – Palpebrate

shellcheck.net was all I needed. many thanks. – Maldon

FWIW, export variable=value is mandated by POSIX: pubs.opengroup.org/onlinepubs/009695399/utilities/export.html. Perhaps it's not available in some ancient shells, but it's definitely not a bashism. – Ronn

I didn't know Heirloom sh, but seem not still active... I often use busybox sh when working in rescue mode... – Selfsufficient

Answer 4

Shell is an interface between a user and OS to access to an operating system's services. It can be either GUI or CLI (Command Line interface).

sh (Bourne shell) is a shell command-line interpreter, for Unix/Unix-like operating systems. It provides some built-in commands. In scripting language we denote interpreter as #!/bin/sh. It was one most widely supported by other shells like bash (free/open), kash (not free).

Bash (Bourne again shell) is a shell replacement for the Bourne shell. Bash is superset of sh. Bash supports sh. POSIX is a set of standards defining how POSIX-compliant systems should work. Bash is not actually a POSIX compliant shell. In a scripting language we denote the interpreter as #!/bin/bash.

Analogy:

• Shell is like an interface or specifications or API.
• sh is a class which implements the Shell interface.
• Bash is a subclass of the sh.

Begot

I don't get it. You've mentioned both "Bash is superset of sh" and "Bash is a subclass of the sh", aren't they contrary statements? Can you please clarify? – Miosis

I think this is trying to say Bash inherits from sh (so it's a "subclass" in the OOP sense) and extends it (so has a superset of the functionality). – Palpebrate

The screen shot is weird; where does it come from? If the "underlying syntax" for Bash is sh, then that should be listed as the underying syntax for ksh too. Conversely, you could argue that the underlying syntax for Bash is ksh, as Bash has borrowed quite liberally from the Korn shell over the years. – Palpebrate

Answer 5

Post from UNIX.COM

Shell features

This table below lists most features that I think would make you choose one shell over another. It is not intended to be a definitive list and does not include every single possible feature for every single possible shell. A feature is only considered to be in a shell if in the version that comes with the operating system, or if it is available as compiled directly from the standard distribution. In particular the C shell specified below is that available on SUNOS 4.*, a considerable number of vendors now ship either tcsh or their own enhanced C shell instead (they don't always make it obvious that they are shipping tcsh.

Code:

                                     sh   csh  ksh  bash tcsh zsh  rc   es
Job control                          N    Y    Y    Y    Y    Y    N    N
Aliases                              N    Y    Y    Y    Y    Y    N    N
Shell functions                      Y(1) N    Y    Y    N    Y    Y    Y
"Sensible" Input/Output redirection  Y    N    Y    Y    N    Y    Y    Y
Directory stack                      N    Y    Y    Y    Y    Y    F    F
Command history                      N    Y    Y    Y    Y    Y    L    L
Command line editing                 N    N    Y    Y    Y    Y    L    L
Vi Command line editing              N    N    Y    Y    Y(3) Y    L    L
Emacs Command line editing           N    N    Y    Y    Y    Y    L    L
Rebindable Command line editing      N    N    N    Y    Y    Y    L    L
User name look up                    N    Y    Y    Y    Y    Y    L    L
Login/Logout watching                N    N    N    N    Y    Y    F    F
Filename completion                  N    Y(1) Y    Y    Y    Y    L    L
Username completion                  N    Y(2) Y    Y    Y    Y    L    L
Hostname completion                  N    Y(2) Y    Y    Y    Y    L    L
History completion                   N    N    N    Y    Y    Y    L    L
Fully programmable Completion        N    N    N    N    Y    Y    N    N
Mh Mailbox completion                N    N    N    N(4) N(6) N(6) N    N
Co Processes                         N    N    Y    N    N    Y    N    N
Builtin artithmetic evaluation       N    Y    Y    Y    Y    Y    N    N
Can follow symbolic links invisibly  N    N    Y    Y    Y    Y    N    N
Periodic command execution           N    N    N    N    Y    Y    N    N
Custom Prompt (easily)               N    N    Y    Y    Y    Y    Y    Y
Sun Keyboard Hack                    N    N    N    N    N    Y    N    N
Spelling Correction                  N    N    N    N    Y    Y    N    N
Process Substitution                 N    N    N    Y(2) N    Y    Y    Y
Underlying Syntax                    sh   csh  sh   sh   csh  sh   rc   rc
Freely Available                     N    N    N(5) Y    Y    Y    Y    Y
Checks Mailbox                       N    Y    Y    Y    Y    Y    F    F
Tty Sanity Checking                  N    N    N    N    Y    Y    N    N
Can cope with large argument lists   Y    N    Y    Y    Y    Y    Y    Y
Has non-interactive startup file     N    Y    Y(7) Y(7) Y    Y    N    N
Has non-login startup file           N    Y    Y(7) Y    Y    Y    N    N
Can avoid user startup files         N    Y    N    Y    N    Y    Y    Y
Can specify startup file             N    N    Y    Y    N    N    N    N
Low level command redefinition       N    N    N    N    N    N    N    Y
Has anonymous functions              N    N    N    N    N    N    Y    Y
List Variables                       N    Y    Y    N    Y    Y    Y    Y
Full signal trap handling            Y    N    Y    Y    N    Y    Y    Y
File no clobber ability              N    Y    Y    Y    Y    Y    N    F
Local variables                      N    N    Y    Y    N    Y    Y    Y
Lexically scoped variables           N    N    N    N    N    N    N    Y
Exceptions                           N    N    N    N    N    N    N    Y

Key to the table above.

Y Feature can be done using this shell.

N Feature is not present in the shell.

F Feature can only be done by using the shells function mechanism.

L The readline library must be linked into the shell to enable this Feature.

Notes to the table above

1. This feature was not in the original version, but has since become almost standard.
2. This feature is fairly new and so is often not found on many versions of the shell, it is gradually making its way into standard distribution.
3. The Vi emulation of this shell is thought by many to be incomplete.
4. This feature is not standard but unofficial patches exist to perform this.
5. A version called 'pdksh' is freely available, but does not have the full functionality of the AT&T version.
6. This can be done via the shells programmable completion mechanism.
7. Only by specifying a file via the ENV environment variable.

Diner

Your table is not useful to me as it tries to compare features of the Bourne Shell and features from ksh from before 1988. If you really make a table for 1988, you would need to remove most of the other shells from that table - including bash, sh and rc. Could you explain where did yo get the values for your table from? – Maximilien

Let me give some hints: Job Control was added to the Bourne Shell in 1989 and the Bourne Shell was made OpenSource in 2005. The Korn shell has process substitution since at least 1988 and it is OpenSource since 1997. BTW: your statements regarding $ENV are not correct, $ENV is only read/executed for interactive shells. – Maximilien

@Maximilien This post has been captured from cs.virginia.edu/helpnet/Computer_OS/unix/shells/shelldiff.html – Diner

@Maximilien If you feel it is incorrect anywhere, please feel free to edit it appropriately. – Diner

Thank you for the pointer! The problem with the table is that it is biased, because it has notice (1) at all but does not use it e.g. for bash. I am sure that we would need to use it for many features of bash but it is not possible anymore to find a reliable source for such a change. Note that the oldest Bourne Shell source is still available, but the oldest bash source I am able to find is for bash-1.14.7 from 1996 Another problem is that the table contains many lines that refer to features I cannot associate with a property, e.g. Mh Mailbox completionor Sun keyboard hack. – Maximilien

So how to deal with such "features"? Also note that shortly after the Bourne Shell was made OpenSource, I started to enhance the Bourne Shell and since 2006, there is e.g. a version with the history editor I designed/prototyped in 1982 and implemented in 1984 for my "bsh" (not Bourne Shell related). BTW: David Korn also started with the Bourne Shell source around 198/1984. – Maximilien

Based on what schily exposed it would seem that it would be better to remove this answer, as it is essentially fraudulent, and OP didn't really vet the information he pasted. – Clericalism

serverfault.com/a/98772/98333 highlights some of the issues with zsh. Bash at least tries to be POSIX if you ask nicely. – Palpebrate

Answer 6

TERMINAL

• program(s) that put a window up
• xterm, rxvt, konsole, kvt, gnome-terminal, nxterm, and eterm.

SHELL

• Is a program that runs in the terminal
• Shell is both a command interpreter and a programming language
• Shell is simply a macro processor that executes commands.
• Macro processor means functionality where text and symbols are expanded to create larger expressions.

SH Vs. BASH

SH

• (SHell)
• Is a specific shell
• a command interpreter and a programming language
• Predecessor of BASH

BASH

• (Bourne-Again SHell)
• Is a specific shell
• a command interpreter and a programming language
• Has sh functionality and more
• Successor of SH
• BASH is the default SHELL

REFERENCE MATERIAL:

SHELL gnu.org:

At its base, a shell is simply a macro processor that executes commands. The term macro processor means functionality where text and symbols are expanded to create larger expressions.

A Unix shell is both a command interpreter and a programming language. As a command interpreter, the shell provides the user interface to the rich set of GNU utilities. The programming language features allow these utilities to be combined. Files containing commands can be created, and become commands themselves. These new commands have the same status as system commands in directories such as /bin, allowing users or groups to establish custom environments to automate their common tasks.

Shells may be used interactively or non-interactively. In interactive mode, they accept input typed from the keyboard. When executing non-interactively, shells execute commands read from a file.

A shell allows execution of GNU commands, both synchronously and asynchronously. The shell waits for synchronous commands to complete before accepting more input; asynchronous commands continue to execute in parallel with the shell while it reads and executes additional commands. The redirection constructs permit fine-grained control of the input and output of those commands. Moreover, the shell allows control over the contents of commands’ environments.

Shells also provide a small set of built-in commands (builtins) implementing functionality impossible or inconvenient to obtain via separate utilities. For example, cd, break, continue, and exec cannot be implemented outside of the shell because they directly manipulate the shell itself. The history, getopts, kill, or pwd builtins, among others, could be implemented in separate utilities, but they are more convenient to use as builtin commands. All of the shell builtins are described in subsequent sections.

While executing commands is essential, most of the power (and complexity) of shells is due to their embedded programming languages. Like any high-level language, the shell provides variables, flow control constructs, quoting, and functions.

Shells offer features geared specifically for interactive use rather than to augment the programming language. These interactive features include job control, command line editing, command history and aliases. Each of these features is described in this manual.

BASH gnu.org:

Bash is the shell, or command language interpreter, for the GNU operating system. The name is an acronym for the ‘Bourne-Again SHell’, a pun on Stephen Bourne, the author of the direct ancestor of the current Unix shell sh, which appeared in the Seventh Edition Bell Labs Research version of Unix.

Bash is largely compatible with sh and incorporates useful features from the Korn shell ksh and the C shell csh. It is intended to be a conformant implementation of the IEEE POSIX Shell and Tools portion of the IEEE POSIX specification (IEEE Standard 1003.1). It offers functional improvements over sh for both interactive and programming use.

While the GNU operating system provides other shells, including a version of csh, Bash is the default shell. Like other GNU software, Bash is quite portable. It currently runs on nearly every version of Unix and a few other operating systems - independently-supported ports exist for MS-DOS, OS/2, and Windows platforms.

Bonaparte

Answer 7

Other answers generally pointed out the difference between Bash and a POSIX shell standard. However, when writing portable shell scripts and being used to Bash syntax, a list of typical bashisms and corresponding pure POSIX solutions is very handy. Such list has been compiled when Ubuntu switched from Bash to Dash as default system shell and can be found here: https://wiki.ubuntu.com/DashAsBinSh

Moreover, there is a great tool called checkbashisms that checks for bashisms in your script and comes handy when you want to make sure that your script is portable.

Dendrochronology

Answer 8

They're nearly identical but bash has more features – sh is (more or less) an older subset of bash.

sh often means the original Bourne shell, which predates bash (Bourne *again* shell), and was created in 1977. But, in practice, it may be better to think of it as a highly-cross-compatible shell compliant with the POSIX standard from 1992.

Scripts that start with #!/bin/sh or use the sh shell usually do so for backwards compatibility. Any unix/linux OS will have an sh shell. On Ubuntu sh often invokes dash and on MacOS it's a special POSIX version of bash. These shells may be preferred for standard-compliant behavior, speed or backwards compatibility.

bash is newer than the original sh, adds more features, and seeks to be backwards compatible with sh. sh programs will usually run just fine in bash. bash is available on nearly all linux/unix machines and usually used by default – with the notable exception of MacOS defaulting to zsh as of Catalina (10.15). FreeBSD, by default, does not come with bash installed.

Losse

sh far predates POSIX. These days, you would hope that any sh you find is at least POSIX-compatible; but on legacy systems this is by no means a given. POSIX stadardizes far more than the shell; in fact, you could argue that the standardization of operating system calls and library functions is more important. – Palpebrate

I removed the stuff about POSIX to make it less confusing – Losse

sh programs should run fine in Bash in practice, not just "in theory". There are obviously corner cases like when a script uses a variable whose name is reserved by Bash but not by other shells. – Palpebrate

Answer 9

/bin/sh may or may not invoke the same program as /bin/bash.

sh supports at least the features required by POSIX (assuming a correct implementation). It may support extensions as well.

bash, the "Bourne Again Shell", implements the features required for sh plus bash-specific extensions. The full set of extensions is too long to describe here, and it varies with new releases. The differences are documented in the bash manual. Type info bash and read the "Bash Features" section (section 6 in the current version), or read the current documentation online.

Melanie

sh only gives you a POSIX shell, if you have the right PATH set up in your current shell. There is no defined PATH-name that gives you a POSIX shell. – Maximilien

For a long time, sh was not necessarily even giving you a POSIX shell, on Solaris, for example. – Palpebrate

Answer 10

The differences explained in the easiest way possible:

After having a basic understanding, the other answers will be easier to understand.

Shell - "Shell" is a program, which facilitates the interaction between the user and the operating system (kernel). There are many shell implementations available, like sh, Bash, C shell, Z shell, etc.

Using any of the shell programs, we will be able to execute commands that are supported by that shell program.

Bash - It derived from Bourne-again Shell. Using this program, we will be able to execute all the commands specified by the shell. Also, we will be able to execute some commands that are specifically added to this program. Bash has backward compatibility with sh.

Sh - It derived from Bourne Shell. "sh" supports all the commands specified in the shell. It means, using this program, we will be able to execute all the commands specified by Shell.

For more information, see:

• dash
• Bash

Protagonist

To understand POSIX, read the response from Alex Please check: https://mcmap.net/q/13465/-what-is-the-meaning-of-quot-posix-quot – Protagonist

I'm not trying to understand POSIX. I'm reviewing your Answer and as such I need to see it your Answer adds value. I do not think it does. – Abirritate

I believe these small clarifications would help a novice to understand the jargon used in the above discussions more comfortably. @Abirritate – Protagonist

Answer 11

The Linux operating system offers different types of shell. Though shells have many commands in common, each type has unique features. Let’s study different kind of mostly used shells.

Sh shell:

Sh shell is also known as Bourne shell. Sh shell is the first shell developed for Unix computers by Stephen Bourne at AT&T's Bell Labs in 1977. It includes many scripting tools.

Bash shell:

Bash shell stands for Bourne Again Shell. Bash shell is the default shell in most Linux distributions and substitute for the Sh shell (the Sh shell will also run in the Bash shell). The Bash shell can execute the vast majority of Sh shell scripts without modification and provide commands line editing feature also.

Prim

There was an earlier shell by Ken Thompson. The Bourne shell was officially introduced in v7 Unix (1979). – Palpebrate