Why Is It Called Bourne Again Shell

What is bash (Bourne Again Shell)?

Bash (Bourne Once again Shell) is the costless and enhanced version of the Bourne shell distributed with Linux and GNU operating systems. Fustigate is similar to the original, merely has added features such as command-line editing.

Created to improve on the earlier Bourne shell (named sh), Fustigate includes features from the Korn crush and the C shell. Bash is intended to conform to the beat standard specified as function of IEEE POSIX. A command language script written for the Bourne shell should likewise run in the bash shell.

Fustigate is released nether the GNU General Public License (GPL), and information technology is available for most versions of Unix and Linux and versions accept been ported to MS-DOS and Windows.

As explained in the Bash Reference Manual, the name fustigate is an acronym of "Bourne-once again SHell" which is a pun on Stephen Bourne, author of the Bourne shell. Bash is a superset of the before shell, and mostly uniform with Bourne shell programs.

What is a vanquish?

In computing, a shell programme provides access to an operating organization's components. The shell gives users (or other programs) a way to go "inside" the system; the shell defines the purlieus between inside and outside.

There are 2 types of operating system shells:

Command-line interface (CLI) shells similar bash offer users a concise and efficient mode of interacting with the Bone, without requiring the overhead of a graphic user interface.
Graphical user interface (GUI) shells, such as Windows and macOS, are considered easier for beginners to apply, but usually also offer programs that emulate a CLI-based shell for arrangement administrators or other ability users who adopt to collaborate at a command prompt.

Bash is the most ordinarily used CLI shell for Unix-based OSes, including Linux.

What is bash used for?

Fustigate, similar other CLIs, is used for whatsoever figurer awarding that requires precision when working with files and data, peculiarly where large numbers of files or large quantities of information need to exist searched, sorted, manipulated or processed in any way.

Some of the most common Bash apply cases include:

Arrangement administrators apply Bash to manage systems systematically and reproducibly. System administrators apply Bash to troubleshoot systems that are not functioning as desired or expected by logging in to systems and reviewing system configurations and network connections. System administrators too rely on Bash scripts to distribute software updates and patches, to monitor running systems, and to update and configure systems.
Software developers rely on Fustigate for many development tasks. Fustigate can be used to automate software development tasks such as code compilation, debugging source lawmaking, change management and software testing.
Network engineers use Bash to test, configure and optimize network operation on organizational networks.
Computer science researchers employ Bash to manage research systems and to bear out research on those systems.
Hobbyists and power users use Fustigate to interact with their systems, execute programs and maintain their systems.

Bash is unremarkably used interactively, merely it can too be used to write shell scripts. About any computer task can be automated using a Bash script. Fustigate scripts can be run on-demand or scheduled to run periodically.

How does bash work?

At first sight bash appears to be a simple command/response organisation, where users enter commands and fustigate returns the results after those commands are run. However, bash is also a programming platform and users are enabled to write programs that accept input and produce output using shell commands in shell scripts.

One of the well-nigh basic bash commands, ls, does one thing: list directory contents. By itself this command lists only the names of files and subdirectories in the current working directory.

Output from bash ls command without parameters — Output from the fustigate ls command includes simply file and directory names.

The ls control has numerous parameters that modify how the results are displayed. Some oft used parameters used with the ls control include:

ls command-line arguments (parameters)	Purpose
-fifty	Use a longer, more detailed, listing format to include file permissions, file possessor, group, size and engagement/time of cosmos.
-a	List all files and subdirectories, even those that are ordinarily intended to be hidden.
-s	Display the size of each file.
-h	Display file and subdirectory sizes in man-readable format using K, M, Thousand and so on to indicate kilobytes, megabytes and gigabytes.
-R	Recursive list of all files and subdirectories nether the electric current working directory.

Used all together, these parameters give the user a much clearer sense of what files and subdirectories are in a directory, when they have last been changed and by whom.

Bash piping pipes — Employ pipes to filter out the desired data from fustigate commands.

Bash enables combining commands past pipage output of i command to be used as the input for another command. For example, this command can exist used to list all files on a file arrangement using the -R parameter to specify the listing should exist recursive:

[email protected]:/$ 1s -1ashR

The response to this command, especially when issued from the arrangement root directory, contains as well many entries for humans to parse hands. This is where pipes tin come into play, in this example, the user can piping the output from the ls command to the Bash text pattern matching command, grep.

The pipage symbol (vertical bar, or "|") directs output from the directory list into the grep command to return only files and subdirectories with filenames that include the specified text design. This command:

[email protected]:/$ 1s -1ashR |grep 'filename.txt'

returns just files that include the string 'filename.txt' so this command can be used to locate a specific file.

Some things that are much easier to practise interactively from the bash command line include:

file and directory management;
checking on network configuration;
editing a configuration file (or whatever text file); and
showing the difference betwixt 2 files.

Types of fustigate commands include:

Simple commands, which unremarkably are run by themselves or with parameters and variables. For instance, the ls command takes parameters too as variables relating to the directories or files to be listed.
Pipes, which are used to link the output of i or more commands every bit input to other commands.
Lists, which enable users to run multiple commands in sequence.
Compound commands, which enable script programming and include loops (for repeating a control a specific number of times) and conditional constructs (for running commands only when a specific condition is met).

Control-line editing is one special fustigate feature not always available with other CLIs. Bash retains a command history, which can be accessed by pressing the up arrow primal. This makes it easier to precisely rerun a command. These prior commands tin also be modified at the command line, using special keys to re-create, paste, delete or modify a prior control.

Bash is ane of the foundations of modernistic organization and network assistants, and new users face up a learning curve when using it. However, in one case learned, fustigate skills are forever: a time-traveling system administrator from 1992 would likely be able to get correct back to work on a modern Linux system, using fustigate. Learn more about how Bash scripting from this tutorial on creating a fustigate shell that accepts arguments when it runs.

This was last updated in December 2021

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