Distinguish between sh and bash in shell

Shell is a command line interpreter in the operating system, mainly used to execute and manage user commands. Common shells include sh, bash, ksh, csh, etc. This article will focus on the differences between sh and bash, two commonly used shells.

First of all, sh and bash are both shells based on the Unix operating system. sh, the Bourne Shell, is the earliest shell version of the Unix system, developed by Stephen Bourne in 1977. And bash, the Bourne-Again Shell, is an extended version of sh, developed by Brian Fox and Chet Ramey in 1989. Therefore, bash contains all the functions of sh, and extends and improves them.

1. Syntax extensions and features
Bash has more syntax extensions and features than sh. For example, bash supports command completion, command history, aliases, parameter expansion, pattern matching and other functions, which sh does not have. These extensions and features make it more convenient and efficient to write and execute commands under bash.

2. Portability
sh is a common shell in Unix systems, and almost all Unix systems have built-in sh. Therefore, scripts written based on sh are very portable and can run on different Unix systems. As an extension to sh, bash is also available on most Unix systems, but not all systems have bash installed by default. On some smaller or embedded Unix systems only sh may be provided. Therefore, in order to ensure the portability of the script, it can be written using sh.

3. Compatibility
bash can be used as a replacement for sh and is fully compatible with sh’s syntax and commands. This means that scripts written in sh can also be run in bash, and can take advantage of more features and syntax extensions in bash. However, sh is not fully compatible with bash's features and syntax extensions. Scripts written using bash's unique syntax and features may not be executed in sh.

4. Speed
Because bash contains more features and extensions, in comparison, the execution speed of bash may be slightly slower than sh. When a large amount of data needs to be processed or execution efficiency needs to be particularly pursued, using sh may be more appropriate. But in general, this speed difference is usually negligible to users.

To sum up, there are certain functional differences between sh and bash. Bash is more powerful and flexible than sh, providing more features and syntax extensions, and is suitable for more complex scripting and command execution. But in some scenarios that require portability, sh is still the first choice. Based on actual needs and operating system support, choosing a suitable shell is very important for writing efficient and portable scripts.

The above is the detailed content of Distinguish between sh and bash in shell. For more information, please follow other related articles on the PHP Chinese website!