File descriptors and redirection in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this redirection command?

Consider the following bash command:

echo 'Hello' 1>&2

What will be the output when you run this command in a terminal?

Bash Scripting

echo 'Hello' 1>&2

A Hello printed to standard error (screen)

B Hello printed to standard output (screen)

C No output, command runs silently

D Syntax error due to incorrect redirection

💡 Hint

Remember that 1 is standard output and 2 is standard error.

The command redirects standard output (file descriptor 1) to standard error (file descriptor 2). So 'Hello' is printed to standard error, which usually appears on the screen but is a different stream than standard output.

💻 Command Output

intermediate

What happens when redirecting both stdout and stderr to a file?

Given this command:

ls /nonexistent /tmp > output.txt 2>&1

What will be the content of output.txt after running it?

Bash Scripting

ls /nonexistent /tmp > output.txt 2>&1

A Only the listing of /tmp directory is saved in output.txt

B Both the error message and the listing of /tmp are saved in output.txt

C Only the error message about /nonexistent is saved in output.txt

D output.txt remains empty

💡 Hint

Think about what 2>&1 means after redirecting stdout.

The command first redirects stdout (1) to output.txt, then redirects stderr (2) to wherever stdout is currently going (output.txt). So both outputs go into output.txt.

📝 Syntax

advanced

Which command correctly appends stderr to a file without affecting stdout?

You want to append only the error messages (stderr) of a command to a file named errors.log, while keeping the standard output visible on the screen. Which command does this correctly?

A command >> errors.log 2>&1

B command > errors.log 2>> errors.log

C command 2> errors.log >> output.log

D command 2>> errors.log

💡 Hint

Appending means using >> and only redirect stderr (2).

Option D appends stderr (2) to errors.log and leaves stdout untouched, so stdout goes to the screen. Option D redirects both stdout and stderr to errors.log. Option D redirects stderr to errors.log but overwrites it, and stdout to output.log. Option D overwrites errors.log with stdout and appends stderr, mixing outputs.

🔧 Debug

advanced

Why does this redirection command produce unexpected output?

Look at this command:

command 2>&1 > output.txt

It produces unexpected output or error. Why?

A Because output.txt does not exist

B Because the order of redirections is correct and should not fail

C Because stderr is redirected to stdout before stdout is redirected to the file

D Because 2>&1 is invalid syntax

💡 Hint

Order of redirections matters in bash.

In bash, redirections are processed left to right. Here, stderr (2) is redirected to where stdout (1) currently points (usually the screen). Then stdout is redirected to output.txt. So stderr still points to the screen, not the file. This causes unexpected output but no syntax error.

🚀 Application

expert

How to redirect stdout to a file and stderr to another file simultaneously?

You want to run a command so that its standard output goes to out.log and its standard error goes to err.log. Which command achieves this correctly?

A command > out.log 2>&1 > err.log

B command 2> err.log > out.log

C command > out.log 2> err.log

D command > out.log 2>&1

💡 Hint

Use separate redirections for stdout and stderr.

Option C redirects stdout to out.log and stderr to err.log separately. Option B also works but order does not matter here. Option A redirects stderr to stdout and then stdout to err.log, mixing outputs. Option D redirects stderr to stdout, so both go to out.log.