File descriptors and redirection in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a file descriptor in bash scripting?

A file descriptor is a number that represents an open file or input/output resource in bash. Common ones are 0 for standard input, 1 for standard output, and 2 for standard error.

beginner

How do you redirect standard output to a file in bash?

Use the > symbol followed by the filename. For example, echo "Hello" > file.txt sends the output to file.txt instead of the screen.

intermediate

What does the command 2>&1 do in bash?

It redirects standard error (file descriptor 2) to the same place as standard output (file descriptor 1). This way, both outputs go to the same destination.

beginner

Explain the difference between > and >> in bash redirection.

> overwrites the file with new output, while >> appends the output to the end of the file without deleting existing content.

intermediate

How can you redirect only standard error to a file, leaving standard output unchanged?

Use 2> filename. For example, command 2> error.log sends error messages to error.log but shows normal output on the screen.

Which file descriptor number represents standard input in bash?

A 0

B 1

C 2

D 3

Standard input is always file descriptor 0.

What does the command ls > files.txt do?

A Appends the list of files to files.txt

B Sends the list of files to the screen

C Sends the list of files to the file files.txt

D Deletes files.txt

The > symbol redirects output to the file, overwriting it.

How do you append output to a file instead of overwriting it?

A >

B <

C 2>

D >>

The >> operator appends output to the file.

What does command 2>&1 do?

A Redirects standard output to standard error

B Redirects standard error to standard output

C Redirects both to a file

D Runs command twice

It sends standard error (2) to the same place as standard output (1).

How to redirect only error messages to a file named error.log?

A command 2> error.log

B command >> error.log

C command > error.log

D command 1> error.log

2> redirects only standard error to the file.

Describe what file descriptors 0, 1, and 2 represent in bash and how you can redirect each.

Think about where data comes from and goes to in commands.

Explain how to combine standard output and standard error into one file using redirection.

Remember the order matters in redirection.