Script security best practices in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to safely check if a file exists before reading it.

Bash Scripting

if [ -f "[1]" ]; then
  cat "[1]"
fi

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

A$filename

B/etc/passwd

Cfilename

D$file

Attempts:

3 left

💡 Hint

Common Mistakes

Using the variable name without $ so it is treated as a string.

Not quoting the variable which can cause errors if it contains spaces.

Using "$filename" ensures the variable is expanded safely and correctly in the test and command.

2fill in blank

medium

Complete the code to prevent running commands from untrusted input.

Bash Scripting

safe_var=$(printf '%q' [1])
echo $safe_var

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

A'$user_input'

B$user_input

Cuser_input

D"$user_input"

Attempts:

3 left

💡 Hint

Common Mistakes

Not using $ so the variable is treated as a literal string.

Adding extra quotes inside the command causing double quoting.

Using "$user_input" with $ expands the variable safely. printf '%q' escapes special characters to prevent code injection.

3fill in blank

hard

Fix the error in the code to safely read a filename from user input.

Bash Scripting

read -r filename
if [[ -n [1] ]]; then
  cat "$filename"
fi

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

A$filename

Bfilename

C"$filename"

D'$filename'

Attempts:

3 left

💡 Hint

Common Mistakes

Checking the variable name as a string instead of its value.

Using quotes incorrectly inside the test.

Using "$filename" with $ inside [[ ]] checks if the variable is not empty safely.

4fill in blank

hard

Fill both blanks to safely loop over filenames with spaces.

Bash Scripting

for file in [1]; do
  echo "Processing: $[2]"
done

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

A"${files[@]}"

Bfiles

Cfile

D"$files"

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted variables causing word splitting.

Using wrong variable names inside the loop.

Using "${files[@]}" expands each element safely preserving spaces. The loop variable is 'file' to access each filename.

5fill in blank

hard

Fill all three blanks to create a secure temporary file and write safely.

Bash Scripting

tmpfile=$(mktemp [1])
echo "Data" > [2]
chmod [3] "$tmpfile"

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

A-t tmp.XXXXXX

B$tmpfile

C600

D-d /tmp

Attempts:

3 left

💡 Hint

Common Mistakes

Not using mktemp options causing insecure temp files.

Writing to wrong file or not using variable.

Setting wrong permissions making file accessible to others.

mktemp with -t creates a temp file with a template. Writing to $tmpfile saves data there. chmod 600 restricts file access to owner only.