stdin redirection (<) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the stdin redirection operator (<) do in Linux command line?

It takes input for a command from a file instead of the keyboard. The command reads data from the file as if it was typed by the user.

beginner

How would you use stdin redirection to provide a file named input.txt as input to the sort command?

You write: sort < input.txt. This tells sort to read its input from input.txt instead of waiting for keyboard input.

intermediate

True or False: Using command < file is the same as cat file | command.

True. Both send the contents of the file as input to the command, but < is simpler and more efficient.

beginner

What happens if you use stdin redirection with a file that does not exist?

The shell will show an error like bash: file: No such file or directory and the command will not run.

beginner

Why is stdin redirection useful in scripting and automation?

It lets scripts read input from files automatically without user typing. This helps run commands on saved data quickly and repeatably.

What does the operator < do in a Linux command?

A Redirects output to a file

B Redirects input from a file to a command

C Pipes output from one command to another

D Runs a command in the background

The < operator takes input from a file and feeds it to the command as if typed by the user.

Which command uses stdin redirection correctly?

A grep 'hello' < file.txt

B grep 'hello' > file.txt

C grep 'hello' | file.txt

D grep 'hello' & file.txt

Option A uses < to send file.txt contents as input to grep.

What error occurs if the file used with < does not exist?

A File is created automatically

B Command runs with empty input

C Command ignores the file and runs normally

D Shell shows 'No such file or directory' error

The shell reports an error because it cannot find the file to redirect input from.

How is < different from a pipe (|)?

A < is for background jobs; | is for input

B < sends output; | sends input

C < sends input from a file; | sends output from a command

D < and | do the same thing

< redirects input from a file; pipe sends output from one command to another.

Why prefer < over cat file | command?

A < is simpler and uses less resources

B cat is faster

C They are exactly the same in all ways

D cat is more secure

< is simpler syntax and more efficient because it avoids creating an extra process.

Explain how stdin redirection (<) works and give a simple example.

Think about how a command reads data without typing.

Describe a situation where stdin redirection helps automate a task.

Imagine you want to process many files quickly.