Bash Input

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Bash Input” Refers to the process of providing commands and data to the Bash shell, which is a popular command line interface and scripting language used primarily in Unix-like operating systems. When you interact with a Bash shell, you can enter various inputs to execute commands, manipulate files, and perform other tasks.

Sources of Bash Input

In the context of Bash, input refers to the data or information that a program receives or reads. And when it comes to a bash script, inputs can originate from various sources:

  • Environment variables: When the parent process starts, these variables are generated & information is stored that can be used in the execution of the scripts.
  • Command-line arguments: When the Bash is executed, these values are given to the script. Normally, they are stored in the positional parameters.
  • Files: The Bash scripts are able to read from the files. They can easily read and extract necessary information from these files for further processing.
  • File Descriptors: A file descriptor serves as a mechanism to interact with different types of input sources, such as pipes, terminals, sockets, and more. These sources enable the script to receive input effectively.

Basics of Bash Script Input

Understanding the origin of input and the desired destination for output is crucial in shell script programming. It involves identifying the source of input, examining its structure and characteristics, and determining the necessary steps or transformations required to produce the desired output. By grasping these concepts, you can effectively manipulate and process data in your shell scripts.

The read command is an important command used for Bash input. Read command provides a lot of arguments that can be passed to it so as to get the user input in a flexible way. Some of the few arguments are shown below.

A few aspects of Bash inputs are given below.

1. Command Line Input

The most common way to provide input to the Bash shell is through the command line. You can type commands, options, arguments, and other parameters directly into the shell prompt. For example, the “bash 2 5” command will pass the 2 and 5 parameters to the bash script.

2. Prompt User to Input

You can develop a bash script that can give a prompt to the terminal for taking input from the user. You can add a timer that will count down the specified time. If the user does not pass any input within that time, the program will be terminated. You can also limit the length of the input so that unnecessarily long input can not be passed as input. You can take a password as input.

3. Standard Input (stdin):

Bash allows you to redirect input from a file to a command using the stdin stream. By default, commands read input from the terminal, but you can use the input redirection operator (“<”) to read from a file instead. For instance, the command ‘sort < input.txt’ reads the contents of ‘input.txt’ and sorts them.

4. Reading a File

As a user, you might need to read a file line from the terminal. Here Bash script will get you cover. You can easily read a file following the below procedures

  • Reading an input file line field-by-field
  • Read text files line-by-line to create pdf files
  • Read from a bash shell variable

5. Taking Input From File

You can take input from

  • Comma Separated Values(CSV) file and to learn more about this read bash read CSV(hyperlink)
  • Text file
  • PDF file

to your bash script. It will ease your task to take multiple and lengthy inputs from the users.

6. Auto-Completion

Bash supports auto-completion, a feature that helps you complete commands, filenames, and other inputs by pressing the Tab key. By configuring auto-completion properly and leveraging Bash’s built-in completion properly and leveraging scripts, you can save time and reduce the likelihood of errors while working with complex or lengthy inputs.

7. Accessing the contents of Files

You can easily access a single file or multiple files and prints the contents to the terminal. Moreover, you can count the total line number of a file. For this purpose, the cat command is used. To learn more about this topic, read cat in Bash (Hyperlink).


In conclusion, mastering Bash’s input capabilities, including command-line arguments, user prompts, input redirection, command substitution, the Readline library, and auto-completion, empowers you to create powerful and interactive scripts, enhancing your command-line experience and productivity.

People Also Ask

[wpsm_accordion] [wpsm_accordion_section title=”What is the standard input in Bash?“]Standard input is used to provide input to a program. (Here we’re using the read built-in to read a line from STDIN.) Standard output is generally used for “normal” output from a command. For example, ls lists files, so the files are sent to STDOUT.[/wpsm_accordion_section] [wpsm_accordion_section title=”Why is it important to validate input in a script?“]It helps prevent malicious users from submitting invalid data. It can help improve application performance since the application doesn’t have to waste time processing invalid data.[/wpsm_accordion_section] [wpsm_accordion_section title=”What are Bash parameters?“]Bash uses a tool called positional parameters to provide a means of entering data into a Bash program when it is invoked from the command line. There are ten positional parameters that run from $0 through $9, although there are ways to hack around that limit.[/wpsm_accordion_section] [wpsm_accordion_section title=”Do bash variables have types?“]Bash comes in two types of variables. Those are system-defined variables and user-defined variables.[/wpsm_accordion_section] [/wpsm_accordion]

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Md. Ashakul Islam Sowad

Hi, I am Md. Ashakul Islam Sowad from Dhaka, Bangladesh. I have completed my undergraduate degree in Biomedical Engineering from the Bangladesh University of Engineering and Technology (BUET). I love to watch football and play video games in my free time. Here, I am working as a Linux Content Developer Executive. Furthermore, as a Linux enthusiast, I am always learning new things about Linux-based systems and I’ll be sharing them here. Read Full Bio

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