How to Create Use on Aix With Bourne Again Shell

What is bash (Bourne Once again Shell)?

Bash (Bourne Once more Shell) is the costless and enhanced version of the Bourne shell distributed with Linux and GNU operating systems. Bash is like to the original, but has added features such equally command-line editing.

Created to improve on the earlier Bourne shell (named sh), Fustigate includes features from the Korn trounce and the C beat out. Bash is intended to conform to the shell standard specified as part of IEEE POSIX. A control linguistic communication script written for the Bourne shell should also run in the bash shell.

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

Equally explained in the Bash Reference Transmission, the proper noun fustigate is an acronym of "Bourne-once again SHell" which is a pun on Stephen Bourne, author of the Bourne crush. Bash is a superset of the earlier shell, and generally compatible with Bourne shell programs.

What is a shell?

In computing, a shell program provides access to an operating organisation's components. The vanquish gives users (or other programs) a way to get "inside" the system; the shell defines the boundary between inside and exterior.

There are two types of operating system shells:

Command-line interface (CLI) shells like bash offer users a curtailed and efficient mode of interacting with the Bone, without requiring the overhead of a graphic user interface.
Graphical user interface (GUI) shells, such equally Windows and macOS, are considered easier for beginners to employ, merely usually also offering programs that emulate a CLI-based trounce for organisation administrators or other power users who prefer to interact at a command prompt.

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

What is bash used for?

Bash, like other CLIs, is used for any estimator application that requires precision when working with files and data, peculiarly where large numbers of files or large quantities of data need to be searched, sorted, manipulated or processed in whatsoever way.

Some of the virtually common Bash use cases include:

Organisation administrators use Bash to manage systems systematically and reproducibly. Organisation 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. Arrangement administrators as well rely on Bash scripts to distribute software updates and patches, to monitor running systems, and to update and configure systems.
Software developers rely on Bash for many development tasks. Bash can be used to automate software development tasks such as code compilation, debugging source code, modify management and software testing.
Network engineers use Bash to examination, configure and optimize network performance on organizational networks.
Computer science researchers use Bash to manage research systems and to bear out inquiry on those systems.
Hobbyists and power users use Bash to collaborate with their systems, execute programs and maintain their systems.

Fustigate is commonly used interactively, but it can also exist used to write shell scripts. Almost whatsoever estimator task can exist automated using a Bash script. Bash scripts tin exist run on-need or scheduled to run periodically.

How does bash work?

At first sight bash appears to exist a unproblematic control/response system, where users enter commands and bash returns the results after those commands are run. However, bash is too a programming platform and users are enabled to write programs that have input and produce output using shell commands in crush scripts.

I of the most basic bash commands, ls, does one thing: list directory contents. By itself this control lists only the names of files and subdirectories in the current working directory.

Output from bash ls command without parameters — Output from the bash ls control includes only file and directory names.

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

ls command-line arguments (parameters)	Purpose
-fifty	Use a longer, more detailed, listing format to include file permissions, file owner, grouping, size and appointment/fourth dimension of creation.
-a	List all files and subdirectories, even those that are commonly intended to be hidden.
-due south	Brandish the size of each file.
-h	Display file and subdirectory sizes in human being-readable format using K, M, Yard and so on to indicate kilobytes, megabytes and gigabytes.
-R	Recursive list of all files and subdirectories nether the 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 past whom.

Bash piping pipes — Use pipes to filter out the desired information from bash commands.

Bash enables combining commands by pipe output of 1 command to exist used every bit the input for another command. For example, this command tin be used to list all files on a file arrangement using the -R parameter to specify the list should be recursive:

[email protected]:/$ 1s -1ashR

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

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

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

returns only 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 do interactively from the fustigate command line include:

file and directory management;
checking on network configuration;
editing a configuration file (or any text file); and
showing the divergence between 2 files.

Types of bash commands include:

Unproblematic commands, which unremarkably are run by themselves or with parameters and variables. For example, the ls command takes parameters every bit well as variables relating to the directories or files to be listed.
Pipes, which are used to link the output of one or more commands as 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 command a specific number of times) and provisional constructs (for running commands simply when a specific status is met).

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

Bash is i of the foundations of modern system and network administration, and new users face a learning curve when using it. However, once learned, bash skills are forever: a fourth dimension-traveling system administrator from 1992 would likely be able to get right back to work on a modern Linux system, using bash. Learn more about how Bash scripting from this tutorial on creating a bash beat out that accepts arguments when it runs.

This was last updated in December 2021