Backticks and $() for command substitution in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of command substitution with backticks

What is the output of this Bash script snippet?

Bash Scripting

current_date=`date +%Y-%m-%d`
echo "Today is $current_date"

A Today is 2024-06-15

B Today is `date +%Y-%m-%d`

C Today is $(date +%Y-%m-%d)

D Syntax error

💡 Hint

Backticks run the command inside and replace it with the output.

The backticks execute the date command and assign its output to the variable. The echo then prints the string with the date.

💻 Command Output

intermediate

Output of command substitution with $()

What will this Bash script print?

Bash Scripting

files_count=$(ls | wc -l)
echo "Number of files: $files_count"

A Number of files: $(ls | wc -l)

B Number of files: ls | wc -l

C Number of files: 5

D Syntax error

💡 Hint

The $() runs the command inside and replaces it with the output.

The command inside $() runs first, counting files, then the result is stored in files_count and printed.

📝 Syntax

advanced

Identify the syntax error in command substitution

Which option contains a syntax error in command substitution?

A output=$ls -l

B output=$(ls -l)

C output=`ls -l`

D `l- sl`=tuptuo

💡 Hint

Command substitution requires backticks or $() around the command.

Option A misses the parentheses or backticks around the command, causing a syntax error.

🔧 Debug

advanced

Why does this command substitution fail?

Given the script: result=`grep 'pattern file.txt` echo "$result" Why does this script fail?

Bash Scripting

result=`grep 'pattern file.txt`
echo "$result"

A No error, runs fine

B Missing closing quote for pattern

C grep command is invalid

D Missing closing backtick

💡 Hint

Check the quotes inside the backticks carefully.

The single quote after pattern is not closed, causing a syntax error inside the command substitution.

🚀 Application

expert

Combine command substitution with arithmetic expansion

What is the output of this Bash script? count=$(ls | wc -l) next=$((count + 1)) echo "Next number is $next"

Bash Scripting

count=$(ls | wc -l)
next=$((count + 1))
echo "Next number is $next"

A Syntax error

B Next number is count + 1

C Next number is $(ls | wc -l + 1)

D Next number is 6

💡 Hint

Command substitution gets the count, arithmetic expansion adds 1.

The script counts files, then adds 1 using arithmetic expansion, then prints the result.