How to Start a Bourne Again Bash Session

What is bash (Bourne Again Shell)?

Bash (Bourne Again Shell) is the free and enhanced version of the Bourne trounce distributed with Linux and GNU operating systems. Bash is similar to the original, but has added features such as control-line editing.

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

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

As explained in the Bash Reference Manual, the proper noun fustigate is an acronym of "Bourne-again Vanquish" which is a pun on Stephen Bourne, author of the Bourne shell. Bash is a superset of the earlier beat, and generally compatible with Bourne shell programs.

What is a beat out?

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

There are two types of operating system shells:

Control-line interface (CLI) shells similar bash offer users a concise and efficient mode of interacting with the OS, 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 use, only usually also offering programs that emulate a CLI-based shell for system administrators or other ability users who prefer to interact at a command prompt.

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

What is bash used for?

Bash, like other CLIs, is used for whatever computer application that requires precision when working with files and information, especially where large numbers of files or big quantities of data need to be searched, sorted, manipulated or processed in any mode.

Some of the most common Bash use cases include:

System administrators use Bash to manage systems systematically and reproducibly. Organisation administrators apply Bash to troubleshoot systems that are non functioning every bit desired or expected by logging in to systems and reviewing system configurations and network connections. Arrangement administrators besides 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. Fustigate tin exist used to automate software evolution tasks such every bit code compilation, debugging source code, change management and software testing.
Network engineers use Bash to exam, configure and optimize network performance on organizational networks.
Informatics researchers use Bash to manage inquiry systems and to carry out enquiry on those systems.
Hobbyists and ability users utilize Bash to interact with their systems, execute programs and maintain their systems.

Bash is ordinarily used interactively, just it can likewise be used to write crush scripts. About any calculator chore can be automated using a Bash script. Bash scripts tin can be run on-need or scheduled to run periodically.

How does bash work?

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

Ane of the most bones fustigate commands, ls, does ane 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 fustigate ls control includes merely 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 control-line arguments (parameters)	Purpose
-l	Utilise a longer, more than detailed, listing format to include file permissions, file owner, group, size and date/time of creation.
-a	List all files and subdirectories, even those that are ordinarily intended to be subconscious.
-s	Display the size of each file.
-h	Display file and subdirectory sizes in homo-readable format using M, Thou, G and then on to indicate kilobytes, megabytes and gigabytes.
-R	Recursive listing of all files and subdirectories under 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 by whom.

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

Fustigate enables combining commands by pipe output of i command to be used equally the input for another command. For example, this command can be used to list all files on a file system using the -R parameter to specify the listing should be recursive:

[e-mail protected]:/$ 1s -1ashR

The response to this command, especially when issued from the system root directory, contains also many entries for humans to parse easily. This is where pipes can come into play, in this case, the user tin pipage the output from the ls command 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 only files and subdirectories with filenames that include the specified text design. This command:

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

returns but 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 direction;
checking on network configuration;
editing a configuration file (or any text file); and
showing the difference between 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 besides as variables relating to the directories or files to exist listed.
Pipes, which are used to link the output of ane 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 conditional constructs (for running commands merely when a specific status is met).

Command-line editing is one special fustigate feature not e'er available with other CLIs. Bash retains a command history, which tin can be accessed by pressing the up pointer key. This makes it easier to precisely rerun a command. These prior commands tin can besides be modified at the control line, using special keys to copy, paste, delete or modify a prior command.

Bash is one of the foundations of modern system and network administration, and new users face up a learning curve when using information technology. However, in one case learned, fustigate skills are forever: a time-traveling system ambassador from 1992 would likely be able to get right dorsum to work on a mod Linux organisation, using bash. Acquire more nigh how Bash scripting from this tutorial on creating a bash crush that accepts arguments when it runs.

This was last updated in December 2021

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