EX200 Create simple shell scripts Practice Test 2 — 15 Questions

Question 1

An administrator writes a script that uses the 'set -e' option at the top. What is the primary effect of this option?

Accepted Answer

It exits the script immediately if a command fails. The 'set -e' option instructs the shell to exit immediately if any command or pipeline returns a non-zero exit status (i.e., fails). This is commonly used in scripts to prevent execution from continuing after an error, which could lead to unpredictable behavior or data corruption. It does not affect variable handling, command printing, or debug verbosity.

Answer

It treats unset variables as an error

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It prints each command before execution

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It enables debug mode with verbose output

Question 2

A system administrator needs to create a shell script that processes a list of hostnames stored in a file, one per line, and runs a command on each host. Which loop construct is most appropriate?

Accepted Answer

while read host; do ... done < hosts. The `while read host; do ... done < hosts` construct reads the file line by line, preserving each hostname exactly as it appears, including spaces or special characters. This is the safest and most idiomatic way to process a list of hostnames in a shell script, as it avoids word splitting and glob expansion issues that can occur with other methods.

Answer

for i in $(seq 1 $(wc -l < hosts)); do ... done

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for host in $(cat hosts); do ... done

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until read host; do ... done < hosts

Question 3

A developer wants to create a script that accepts a directory path as an argument and creates a timestamped backup of that directory. If no argument is provided, it should back up the current directory. How should the script handle the argument?

Accepted Answer

dir=${1:-.}. `${1:-.}` uses the default value substitution syntax in bash: if parameter `$1` (the first positional argument) is unset or null, it expands to `.` (the current directory). This ensures the script backs up the supplied directory path or defaults to the current directory when no argument is provided, exactly matching the requirement.

Answer

dir=${@:-.}

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dir=${0:-.}

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dir=${?:-.}

Question 4

An administrator writes a script to check disk usage and send an alert if usage exceeds 80%. The script uses 'df -h /' and parses the output. To maintain portability and avoid common pitfalls, which approach is recommended?

Accepted Answer

Use 'df / | awk 'NR==2 {print $5}' | tr -d '%'. It uses `df /` (without `-h`) to produce a stable, machine-parseable output where the fifth field (`$5`) is always the percentage used, and `awk` reliably extracts it. The `tr -d '%'` removes the percent sign for numeric comparison. This approach avoids the portability issues of parsing human-readable output from `df -h`, which can vary in column spacing and ordering across different Unix/Linux systems.

Answer

Use 'df -h / | tail -1 | sed 's/.* //' | tr -d '%'

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Use 'df -h / | tail -1 | cut -d' ' -f5'

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Use 'df -h / | grep -oP '\d+%'

Question 5

A script needs to execute a command that might fail, but the script should continue. The administrator wants to capture the exit status for logging. Which code snippet correctly implements this?

Accepted Answer

./risky_command; rc=$?; echo $rc. It runs the risky command, captures its exit status immediately after in the `$?` variable, and then echoes it for logging. The script continues regardless of the command's success or failure, which meets the requirement. The `$?` variable holds the exit status of the last executed foreground command, so assigning it to `rc` right after `./risky_command` ensures the correct value is stored.

Answer

set -e; ./risky_command; rc=$?; echo $rc

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rc=$? ./risky_command; echo $rc

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./risky_command && rc=$?; echo $rc

Question 6

A complex script uses 'trap' to handle signals. The admin writes 'trap '' SIGINT' to ignore Ctrl+C, but later in the script they want to re-enable the default behavior. Which command restores the default behavior for SIGINT?

Accepted Answer

trap - SIGINT. `trap - SIGINT` resets the signal handler for SIGINT to its default behavior. The `trap '' SIGINT` command sets an empty action, which ignores the signal; using `trap - signal` removes that custom handler and restores the default action (typically terminating the process).

Answer

trap : SIGINT

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trap 2

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trap SIGINT

Question 7

Which THREE of the following are common practices to improve the reliability of shell scripts?

Accepted Answer

Always quote variable expansions unless word splitting is intended. Option A is correct because quoting variable expansions such as "$var" prevents unintended word splitting and glob expansion, which are common sources of bugs and failures in shell scripts. Option C is correct because 'set -u' causes the shell to treat references to unset variables as an error and exit, catching typos and missing environment variables early. Option D is correct because 'set -e' makes the script exit immediately when a command returns a non-zero status, preventing execution from continuing after a failure. Option B is not a reliability practice: 'echo "Error"' without redirection writes to stdout rather than stderr, so error messages may be missed or mixed with normal output. Option E is not recommended: using 'cat' to feed a while loop spawns an extra process and is less efficient than redirecting the file directly into the loop, and it does not by itself improve reliability.

Answer

Use 'echo "Error"' for error messages without redirection

Answer

Use 'cat' to read files line by line in while loops

Question 8

Which TWO of the following are correct statements about exit codes in shell scripts?

Accepted Answer

A non-zero exit code usually indicates a failure. In shell scripting, exit codes are integers from 0 to 255. An exit code of 0 conventionally indicates success, while any non-zero value (1–255) indicates a failure or error condition. Option B is correct because a non-zero exit code usually signals that the command or script did not complete successfully.

Answer

An exit code of 1 means success

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An exit code of -1 indicates a system error

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If no 'exit' is used, the script exits with code 0

Question 9

Consider the script in the exhibit. The script is run in a directory containing 'a.txt' and 'b.txt' but also has a subdirectory 'backup' with .txt files. What will be the output?

Accepted Answer

Line counts for 'a.txt' and 'b.txt' only. The script uses `for i in *.txt`, which by default only matches .txt files in the current directory, not in subdirectories. Since 'a.txt' and 'b.txt' are in the current directory, the loop iterates over them and runs `wc -l` on each, outputting their line counts. The 'backup' subdirectory is not traversed because the glob pattern does not include paths with directories.

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An error because the for loop cannot iterate over files with spaces

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Line counts for .txt files in 'backup' only

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Line counts for all .txt files including those in 'backup'

Question 10

A developer runs the script shown in the exhibit and always sees 'Success' printed, even when the previous command fails. What is the most likely cause?

Accepted Answer

The $? variable captures the exit status of the [[ command, not the intended command. The `[[ ]]` conditional construct is a shell keyword that itself produces an exit status. When `$?` is checked immediately after `[[ ]]`, it captures the exit status of the `[[ ]]` evaluation (which is 0 if the condition is true, 1 if false), not the exit status of the command that was run before the `[[ ]]`. Since the developer always sees 'Success' printed, the `[[ ]]` condition must be evaluating to true (exit status 0), causing `$?` to be 0 and the script to always take the success path, regardless of the actual previous command's result.

Answer

The [[ ]] syntax always evaluates to true

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The $? variable is only set after external commands, not builtins

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The $? variable always returns 0 in a conditional

Question 11

A user executes the script shown in the exhibit with './export_script.sh' and then runs 'echo $MY_VAR' in the same terminal. The output is empty. Why does this happen?

Accepted Answer

The script runs in a sub-shell, so exported variables are not available to the parent shell. When a script is executed with './export_script.sh', it runs in a sub-shell (a child process). The 'export' command within the script makes the variable available to that sub-shell and its own child processes, but not to the parent shell that invoked the script. Therefore, after the script exits, the variable MY_VAR is not defined in the parent shell's environment, resulting in an empty output from 'echo $MY_VAR'.

Answer

The script lacks execute permissions

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The 'export' command is incorrectly placed after the variable assignment

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The variable name should be in uppercase for it to be inherited

Question 12

A script contains: lines=$(wc -l /etc/passwd); echo $((lines+1)). The output is unexpected. What is the problem?

Accepted Answer

lines contains a string including the filename, not just a number.. The command substitution `$(wc -l /etc/passwd)` outputs the line count followed by a space and the filename `/etc/passwd`. This entire string (e.g., `35 /etc/passwd`) is stored in the variable `lines`. When `$((lines+1))` attempts arithmetic expansion, it fails because the string is not a pure integer, causing the shell to treat it as 0 or produce an error, resulting in an unexpected output.

Answer

wc -l requires the -c option to count correctly.

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The script has a syntax error in the echo command.

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$((...)) cannot read a variable from command substitution.

Question 13

A script has a syntax error. Which command will help identify the line number of the error without executing the script?

Accepted Answer

bash -n script.sh. The `bash -n` (noexec) option performs syntax checking on a script without executing any commands. If a syntax error exists, Bash reports the error along with the line number, making it the correct tool for identifying syntax errors in a script without running it.

Answer

which bash

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set -x

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bash -v script.sh

Question 14

Which shell built-in can be used to read user input during script execution?

Accepted Answer

read. The `read` built-in command is specifically designed to capture user input from standard input (stdin) during script execution, storing it in one or more variables. This makes it the correct choice for interactive scripts that require runtime input from the user.

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printf

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cat

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echo

Question 15

A script needs to read every line from a file and execute a command on each line. Which code block is correct and handles whitespace correctly?

Accepted Answer

while IFS= read -r line; do echo "$line"; done < file.txt. It uses `IFS=` to preserve leading/trailing whitespace and `-r` to prevent backslash interpretation, ensuring each line is read exactly as it appears in the file. The `< file.txt` redirect feeds the file line by line into the `while` loop, which is the standard and safe method for line-by-line processing in Bash.

Answer

while IFS=$'
' read line; do echo "$line"; done <<< file.txt

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while read line; do echo $line; done < file.txt

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for line in $(cat file.txt); do echo $line; done