set -x for trace mode in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output when using set -x in a simple script?

Consider this bash script snippet:

#!/bin/bash
set -x
x=5
y=3
z=$((x + y))
echo $z

What will be printed to the terminal when this script runs?

Bash Scripting

#!/bin/bash
set -x
x=5
y=3
z=$((x + y))
echo $z

A

+ x=5
+ y=3
+ z=8
8

B 8

C

+ x=5
+ y=3
+ z=8
+ echo 8
8

D

x=5
y=3
z=8
echo 8
8

💡 Hint

Trace mode prints each command with a plus sign before executing it.

The set -x command enables trace mode, which prints each command preceded by a plus sign (+) before it runs. So you see the assignments and the echo command with +, then the output 8.

💻 Command Output

intermediate

What happens if set -x is turned off mid-script?

Given this bash script:

#!/bin/bash
set -x
var=10
set +x
var2=20
echo $var $var2

What will be the output including trace lines?

Bash Scripting

#!/bin/bash
set -x
var=10
set +x
var2=20
echo $var $var2

A

+ var=10
var2=20
10 20

B

+ var=10
+ set +x
+ var2=20
+ echo 10 20
10 20

C

var=10
var2=20
10 20

D

+ var=10
var2=20
+ echo 10 20
10 20

💡 Hint

set +x disables trace mode, so commands after it won't show trace.

Trace mode is on until set +x disables it. So only the first assignment shows with +, the second does not. The echo command still runs and prints 10 20.

🔧 Debug

advanced

Why does this script not show trace output after set -x?

Look at this script:

#!/bin/bash
set -x
if false; then
  echo "Won't run"
fi
set +x
echo "Done"

Why is there no trace output for the echo inside the if block?

Bash Scripting

#!/bin/bash
set -x
if false; then
  echo "Won't run"
fi
set +x
echo "Done"

A Because the if condition is false, the echo inside never runs, so no trace output.

B Because set -x only traces commands outside if blocks.

C Because set -x was disabled before the if block.

D Because echo commands are never traced.

💡 Hint

Trace shows commands that actually run.

The echo inside the if block is skipped since the condition is false. So no trace output appears for it.

💻 Command Output

advanced

What is the output of this script with nested set -x and set +x?

Analyze this script:

#!/bin/bash
set -x
var=1
{
  set +x
  var=2
  echo $var
}
echo $var

What is the full output including trace lines?

Bash Scripting

#!/bin/bash
set -x
var=1
{
  set +x
  var=2
  echo $var
}
echo $var

A

+ var=1
var=2
2
+ echo 2
2

B

+ var=1
var=2
2
+ echo 2
+ echo 2
1

C

+ var=1
var=2
2
+ echo 2
+ echo 2
2

D

+ var=1
var=2
2
+ echo 2
+ echo 2
+ echo 2
2

💡 Hint

set +x disables trace inside the block, but echo outside still traces.

Trace is on initially, so var=1 shows with +. Inside the block, set +x disables trace, so var=2 and echo $var run silently printing 2. After block, echo $var runs with trace showing + echo 2 and prints 2.

🧠 Conceptual

expert

How does set -x help in debugging complex scripts?

Which of these best explains the main benefit of using set -x in bash scripts?

A It automatically fixes syntax errors in the script.

B It shows each command and its arguments as they are executed, helping to trace script flow and spot errors.

C It runs the script faster by optimizing commands.

D It hides sensitive information from the output.

💡 Hint

Think about what trace mode does when enabled.

set -x prints each command with its arguments before running it, so you can see exactly what the script does step-by-step. This helps find where things go wrong.