File descriptors and redirection in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to redirect standard output to a file named output.txt.

Bash Scripting

echo "Hello World" [1] output.txt

Drag options to blanks, or click blank then click option'

A>>

B2>

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using >> appends instead of overwriting.

Using < redirects input, not output.

The > operator redirects standard output to a file, overwriting it.

2fill in blank

medium

Complete the code to append standard output to a file named log.txt.

Bash Scripting

ls -l [1] log.txt

Drag options to blanks, or click blank then click option'

A>

B>>

C2>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using > overwrites the file instead of appending.

Using 2> redirects standard error, not standard output.

The >> operator appends output to the file without overwriting.

3fill in blank

hard

Fix the error in the code to redirect standard error to errors.log.

Bash Scripting

grep 'pattern' file.txt [1] errors.log

Drag options to blanks, or click blank then click option'

A2>

B>

C>>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using > redirects standard output, not error.

Using < redirects input, not error output.

The 2> operator redirects standard error (file descriptor 2) to a file.

4fill in blank

hard

Fill both blanks to redirect standard output to out.txt and standard error to err.txt.

Bash Scripting

command [1] out.txt [2] err.txt

Drag options to blanks, or click blank then click option'

A>

B2>

C>>

D2>>

Attempts:

3 left

💡 Hint

Common Mistakes

Using append operators >> or 2>> when overwriting is needed.

Mixing up standard output and error redirection operators.

> redirects standard output, and 2> redirects standard error.

5fill in blank

hard

Fill all three blanks to redirect standard output to output.log, standard error to error.log, and append standard output to combined.log.

Bash Scripting

my_script.sh [1] output.log [2] error.log [3] combined.log

Drag options to blanks, or click blank then click option'

A>

B2>

C>>

D2>>

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2>> for standard error when overwriting is needed.

Confusing append and overwrite operators.

> overwrites standard output, 2> overwrites standard error, and >> appends standard output.

Practice

1. Which file descriptor number represents the standard error stream in bash?

easy

A. 3

B. 1

C. 2

D. 0

Solution

1. Step 1: Recall standard file descriptors

   Standard input is 0, standard output is 1, and standard error is 2.

2. Step 2: Identify the error stream descriptor

   The error stream is always file descriptor 2 in bash.

3. Final Answer:

   2 -> Option C

4. Quick Check:

   Standard error = 2 [OK]

Hint: Remember: 0=input, 1=output, 2=error [OK]

Common Mistakes:

• Confusing standard output (1) with error (2)
• Thinking input (0) is error
• Using non-standard descriptor numbers

2. Which of the following is the correct syntax to redirect standard output to a file named output.txt in bash?

easy

A. command >> output.txt 2>&1

B. command < output.txt

C. command 2> output.txt

D. command > output.txt

Solution

1. Step 1: Understand output redirection syntax

   Using > redirects standard output (file descriptor 1) to a file, overwriting it.

2. Step 2: Match syntax to redirect output only

   command > output.txt uses > correctly to redirect output to output.txt.

3. Final Answer:

   command > output.txt -> Option D

4. Quick Check:

   Output redirection uses > [OK]

Hint: Use > for output, < for input redirection [OK]

Common Mistakes:

• Using < instead of > for output
• Redirecting error (2>) instead of output
• Appending (>>) when overwrite is needed

3. What will be the output of the following command if file.txt does not exist?

cat file.txt > output.txt 2>&1

medium

A. Redirects both output and error messages to output.txt

B. Creates an empty output.txt file with no error message

C. Outputs the error message to the terminal and creates output.txt

D. Throws a syntax error and does nothing

Solution

1. Step 1: Understand redirection 2>&1

   This redirects standard error (2) to the same place as standard output (1).

2. Step 2: Analyze command behavior when file missing

   cat tries to read file.txt, fails, and sends error to stderr, which is redirected to output.txt along with stdout.

3. Final Answer:

   Redirects both output and error messages to output.txt -> Option A

4. Quick Check:

   2>&1 merges error into output [OK]

Hint: 2>&1 sends errors to the same place as output [OK]

Common Mistakes:

• Thinking error shows on terminal
• Assuming output.txt stays empty
• Confusing 2>&1 with separate redirections

4. Identify the error in this command that attempts to redirect only standard error to error.log:

ls -l > error.log 2>

medium

A. Output redirection > should be 1>

B. Missing filename after 2> for error redirection

C. Should use 2>&1 instead of 2>

D. Command syntax is correct

Solution

1. Step 1: Check error redirection syntax

   Redirection 2> must be followed by a filename to redirect standard error.

2. Step 2: Identify missing filename

   The command ends with 2> but no file is specified, causing a syntax error.

3. Final Answer:

   Missing filename after 2> for error redirection -> Option B

4. Quick Check:

   2> needs a target file [OK]

Hint: Always specify a file after 2> for error redirection [OK]

Common Mistakes:

• Leaving out filename after 2>
• Confusing 2> with 2>&1
• Thinking > needs to be 1>

5. You want to run a script that outputs normal messages to output.log and error messages to error.log. Which command correctly achieves this?

hard

A. ./script.sh > output.log 2> error.log

B. ./script.sh 2>&1 > output.log error.log

C. ./script.sh > output.log 2>&1 error.log

D. ./script.sh > output.log &> error.log

Solution

1. Step 1: Understand separate redirection for output and error

   To send stdout and stderr to different files, use > for stdout and 2> for stderr separately.

2. Step 2: Analyze each option

   ./script.sh > output.log 2> error.log correctly redirects stdout to output.log and stderr to error.log. Others mix or misuse redirection syntax.

3. Final Answer:

   ./script.sh > output.log 2> error.log -> Option A

4. Quick Check:

   Separate > and 2> for output and error [OK]

Hint: Use > for output, 2> for errors to separate files [OK]

Common Mistakes:

• Using &> redirects both to one file
• Mixing order of redirections incorrectly
• Omitting file names after redirection operators