These include things like scoped local variables and arrays. Plain sh is a very minimalistic programming language. 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. 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. 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. The Bash Reference manual has a section which attempts to enumerate the differences but some common sources of confusion include. Remember, this is an abridged listing. A common error is to have a! This basically disables any Bash-only functionality, so you get syntax errors e.
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. Shell is an interface between a user and OS to access to an operating system's services. It provides some built-in commands. In scripting language we denote interpreter as! Bash B ourne a gain s hell is a shell replacement for the Bourne shell. Bash is superset of sh.
Bash supports sh. In a scripting language we denote the interpreter as! 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.
SHELL gnu. 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. 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. 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. Bash is the shell, or command language interpreter, for the GNU operating system. Bash is largely compatible with sh and incorporates useful features from the Korn shell ksh and the C shell csh. 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. 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. 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. Basically bash is sh, with more features and better syntax. Most commands work the same, but they are different. Bash bash is one of many available yet the most commonly used Unix shells.
Shell scripting is scripting in any shell, whereas Bash scripting is scripting specifically for Bash. In practice, however, "shell script" and "bash script" are often used interchangeably, unless the shell in question is not Bash. I would use bash, as that is pretty much the standard or at least most common, from my experience. In fact, problems arise when a bash script will use! They're nearly identical but bash has more features — sh is more or less an older subset of bash.
But, in practice, it may be better to think of it as a highly-cross-compatible shell compliant with the POSIX standard from Scripts that start with! These shells may be preferred for standard-compliant behavior, speed or backwards compatibility. In theory, sh programs should run in bash.
FreeBSD, by default, does not come with bash installed. It may support extensions as well. 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. But in all these, it is advisable to use sh because sh is standardized, simpler, and easy to learn. On the other hand, bash has its advantages, mostly because it is more programmer-friendly than sh.
Bash features make programming easier, and they are similar to what you get from contemporary programming languages. Ever come across a scenario where you need to access a Linux partition from a Windows PC? DiskInternals Linux Reader can help you in this regard.
More importantly they also include programming constructs like conditional operations if, then, else, for loops, while loops, ways to check the status returned when you run a statement e. These are the foundations of more complex command line shell scripts, and in fact is what the command line interpreter is. You could think of it as being short for 'Bash Shell Interpreter'.
Over the years it has become customary to refer to the particular command line interpreter you are using as the shell because one can't be used without the other. But the reality is that they are different. As to why they are properly known as command line interpreters and not as the actual shell: it is because they live in the shell and interpret all commands as if they were running in a program. And the shell doesn't care what interpreter you run in it, as long as it meets the correct standards.
And as to why they are called interpreters, it is because they are really interpreters. Even if you are not explicitly running a script and a script is really just a text file of commands you create so that you can execute the same commands over and over without having to type them in again. For example, take the humble 'ls' command. When you run it, it returns a list of files. But how it runs is more important to your question: It actually runs inside the context of the command line interpreter, even if you just run what appears to be a simple one off command.
That is, it runs as if it were a statement in part of a bigger program. It runs as if it were in a shell script script file without actually being in a shell script file. An anonymous shell script file as it were. Anything you run on the command line has this in common whether it be a single command like 'ls' or a script file full of commands and iterators and conditional statements : it is all processed by the command line interpreter; be it Bash, C-Shell, K-Shell default on AIX btw.
You should see it return a number it should be '2'. That is the return code from grep that means 'no such file or directory'. Now run the following:. You will see the file 'hello. Even if these seemingly one off commands are run, the command line interpreter acts like they are part of a larger program and keeps track of their return values.
It is knows the statement is incomplete and expects more input. After all you could conceivably be going to ask it to grep the results of some loop which is perfectly legal to write and run on the command line.
Bottom line is the shell is the shell, and the interpreter whatever the name of the one you use, 'Bash', k-shell, etc. But often they are used interchangeably, because at any given instant they are completely tied together.
By example, on Minix3 , there's the ash shell, it doesn't support associative arrays like bash4. All shells have their similarities and differences.
For example a script written in bash, might be fully or largely compatible with another shell for example zsh. Due to the fact that bash is very widespread, it is often implied that a script is compatible with it. If you're looking to buy a book, buy one written specifically for the shell you intend to use. It would be a good idea to read up on their differences before spending money though. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Learn more. What's the difference between the terms "Shell" and "Bash"? Ask Question. Asked 9 years, 1 month ago. Active 9 years ago. Viewed 18k times. What is the the difference between "Shell" and "Bash" and what do these terms mean? Improve this question. Hen R. Hen 1 1 gold badge 1 1 silver badge 5 5 bronze badges.
0コメント