What is standard input?

Standard input (stdin) is a stream from which a program reads its input data. In most operating systems, including Unix and Linux, standard input is typically associated with the keyboard. When a program is executed, it can receive input from the user through stdin.

Key Points:

1. Default Source: By default, stdin is connected to the keyboard, allowing users to type input directly into the terminal.

2. Redirection: Stdin can be redirected from files or other commands using input redirection operators. For example:

   command < inputfile.txt

   This command will take the contents of inputfile.txt as input for command.

3. Pipes: Stdin can also receive input from the output of another command using pipes. For example:

   command1 | command2

   Here, the output of command1 is sent as input to command2.

4. Usage in Programming: In programming, stdin is often used to read user input or data from files, making it a fundamental concept in command-line interfaces and scripting.

Overall, standard input is a crucial part of how programs interact with users and other processes in a computing environment.