Subshells (command grouping) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this subshell command?

Consider the following bash script snippet. What will be printed to the terminal?

Bash Scripting

count=5
(echo $count; count=10; echo $count)
echo $count

A

5
5
5

B

5
10
10

C

5
10
5

D

10
10
10

💡 Hint

Remember that commands inside parentheses run in a subshell, so variable changes inside do not affect the parent shell.

The variable 'count' is initially 5. Inside the subshell, it prints 5, then changes to 10 and prints 10. Outside, the original 'count' remains 5, so the last echo prints 5.

💻 Command Output

intermediate

How many lines will this command output?

What is the number of lines printed by this command? (echo "line1"; echo "line2"; echo "line3") | wc -l

Bash Scripting

(echo "line1"; echo "line2"; echo "line3") | wc -l

A Error

B 1

C 0

D 3

💡 Hint

The subshell groups commands and pipes their combined output to wc -l.

The subshell runs three echo commands, each printing a line. The pipe sends all three lines to wc -l, which counts lines and outputs 3.

🔧 Debug

advanced

Why does this script print '0' instead of '3'?

This script intends to count files but prints 0. Why? count=0 (ls *.txt; count=$(ls *.txt | wc -l)) echo $count

Bash Scripting

count=0
(ls *.txt; count=$(ls *.txt | wc -l))
echo $count

A Because 'count' is set inside a subshell, it does not affect the parent shell variable.

B Because 'ls *.txt' returns no files, so count is zero.

C Because the syntax for command substitution is incorrect.

D Because 'echo $count' is inside the subshell and prints zero.

💡 Hint

Think about where variable assignments inside parentheses take effect.

The parentheses create a subshell. Variable assignments inside it do not change the parent shell's variables. So 'count' outside remains 0.

🚀 Application

advanced

Which command correctly groups commands to redirect combined output?

You want to run two commands and redirect both their outputs to a file. Which option does this correctly?

A echo "Hello"; echo "World" > output.txt

B (echo "Hello"; echo "World") > output.txt

C echo "Hello" > output.txt; echo "World" > output.txt

D { echo "Hello"; echo "World"; } > output.txt

💡 Hint

Grouping commands with parentheses runs them in a subshell and redirects all output together.

Option B runs both echo commands in a subshell and redirects all output to the file once. Option B uses braces which also groups commands but requires spaces and a semicolon; however, the question asks for subshell grouping.

🧠 Conceptual

expert

What is the effect of this command on the variable 'var'?

Given this script: var=1 (var=5; echo $var) echo $var What will be printed and why?

Bash Scripting

var=1
(var=5; echo $var)
echo $var

A

5
1
Because the assignment inside the subshell does not affect the parent shell variable.

B

1
1
Because the subshell does not print anything.

C

1
5
Because the first echo is outside the subshell.

D

5
5
Because the variable is changed globally.

💡 Hint

Variables changed inside parentheses do not change outside variables.

The subshell changes 'var' to 5 and prints it. Outside, 'var' remains 1, so the last echo prints 1.