EX200 Create simple shell scripts Practice Test 2 — 15 Questions

Question 1

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.

Answer

printf

Answer

cat

Answer

echo

Question 2

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

Answer

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

Answer

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

Question 3

Which TWO methods correctly create a variable containing the number of regular files in the current directory (excluding . and ..)?

Accepted Answer

count=$(find . -maxdepth 1 -type f -printf '.' | wc -c). Both B and E use `find . -maxdepth 1 -type f` to select only regular files in the current directory, excluding . and .. . Option B prints a dot per file and counts bytes, giving a count that is unaffected by newlines in filenames. Option E lists each file path on its own line and counts lines; it works for normal filenames but may miscount if filenames contain newlines. Both are valid methods for the task.

Answer

count=$(ls -1A | wc -l)

Answer

count=$(stat -c%F * | grep -c 'regular file')

Answer

count=$(ls -1 | wc -l)

Question 4

Which THREE of the following are valid and recommended practices when writing shell scripts for RHEL?

Accepted Answer

Using 'local' keyword for variable declarations inside functions.. The 'local' keyword restricts a variable's scope to the function where it is declared, preventing unintended side effects on global variables. This is a recommended practice in RHEL shell scripting to maintain modularity and avoid namespace pollution.

Answer

Using 'set -e' to exit on non-zero exit codes.

Answer

Using the 'source' command instead of '.' for readability.

Question 5

Refer to the exhibit. The script produces the error shown. What is the most likely cause?

Accepted Answer

The variable $var is empty or unset.. The error 'unary operator expected' occurs in bash when the `[ ]` test command encounters an empty or unset variable on the left side of a comparison operator. Since `$var` is empty, the expression `[ $var = 'value' ]` expands to `[ = 'value' ]`, which is syntactically invalid because the `=` operator expects a left operand. Option D correctly identifies this as the root cause.

Answer

The = operator should be == for string comparison.

Answer

The string 'value' contains spaces.

Answer

The script is missing a valid shebang.

Question 6

You are tasked with creating a script that reads a list of usernames from /tmp/users.txt, one per line, and creates a home directory for each user using `mkdir /home/$username`. The script is:

#!/bin/bash
while read username; do
  mkdir /home/$username
done < /tmp/users.txt

However, the script fails for usernames that contain spaces (e.g., 'john smith'). The error is 'mkdir: cannot create directory '/home/john': File exists' and then a separate directory for 'smith'. What is the best fix?

Accepted Answer

Use `while IFS= read -r username` to preserve the line as is.. Setting `IFS=` (to an empty value) before the `read` command prevents the shell from splitting the line into fields based on whitespace. The `-r` option prevents backslash escapes from being interpreted. Together, they ensure that each line from the file is read exactly as is, preserving spaces in usernames. Option B is not sufficient because even though quoting `$username` prevents word splitting in the `mkdir` command, the `read` command itself splits the line before the variable is assigned, so the username is already broken into multiple words. Option A changes to a `for` loop that iterates over the output of `cat`, which also splits on whitespace and is subject to pathname expansion. Option C disables pathname expansion (globbing) but does not affect word splitting by `read`.

Answer

Change the loop to `for username in $(cat /tmp/users.txt)`.

Answer

Quote $username in the mkdir command as in `mkdir "/home/$username"`.

Answer

Add `set -f` to disable pathname expansion.

Question 7

A new intern created a script to display the current user's home directory:

#!/bin/bash
echo "Home directory: $home"

The script outputs 'Home directory: ' with nothing after the colon. What is the most likely cause?

Accepted Answer

There is a typo: it should be $HOME, not $home.. Bash is case-sensitive, and the variable should be $HOME, not $home. The environment variable HOME is set for all users and contains the path to their home directory. The script uses $home (lowercase), which is not a standard environment variable and is likely unset, resulting in an empty output. Option A is incorrect because HOME is typically set in the environment. Option C is incorrect because both sh and bash set the HOME variable, so using sh would not cause the issue. Option D is incorrect because the root user has a home directory (usually /root), and the issue is the variable name, not the user.

Answer

The HOME variable is not set in the environment.

Answer

The script is run with 'sh' instead of 'bash'.

Answer

The root user has no home directory.

Question 8

A system administrator writes a shell script to monitor disk usage and send an alert if any partition exceeds 80%. Which TWO of the following are best practices for implementing this script?

Accepted Answer

Include error handling to check for missing commands and exit gracefully.. Robust shell scripts should always include error handling to verify that required commands (e.g., `df`, `awk`, `grep`) are available before proceeding. This prevents the script from failing silently or producing misleading output, and allows it to exit gracefully with a meaningful error message, which is a key best practice for production scripts.

Answer

Use `cat /proc/partitions` to retrieve partition sizes.

Answer

Send alerts only via syslog (logger command).

Answer

Use `du -h /` and parse the output.

Question 9

A system administrator writes the script shown. The /etc directory contains .conf files with spaces in their names (e.g., "my config.conf"). What is the most accurate description of the script's behavior?

Accepted Answer

The script will split filenames with spaces into multiple words, causing errors.. The script uses a for loop with `for file in /etc/*.conf`, which relies on shell globbing. When the glob expands, filenames with spaces (e.g., "my config.conf") are treated as separate words due to word splitting, causing the loop to iterate over each word rather than each file. This results in errors when commands like `echo` or `cp` receive broken paths.

Answer

The script will correctly process all .conf files, including those with spaces.

Answer

The script will only process the first .conf file and then exit.

Answer

The script will not execute because of a syntax error.

Question 10

An organization uses a shell script that runs daily via cron on a central management server to archive logs from 50 remote Red Hat Enterprise Linux servers. The script uses `scp` with SSH key-based authentication (passwordless) to transfer files. Recently, after a security team rotated the SSH host keys on all remote servers, the script started failing with 'Host key verification failed' errors. The administrator needs to restore automated log transfers without compromising security. The remote servers are in a controlled internal network, and the management server's `~/.ssh/known_hosts` file is not centrally managed. Which course of action should the administrator take?

Accepted Answer

Use ssh-keyscan to retrieve the new host keys and add them to the management server's known_hosts file.. Using `ssh-keyscan` to retrieve the new host keys and add them to the management server's `known_hosts` file is the proper method to update host keys without disabling security. This approach maintains SSH host key verification, which prevents man-in-the-middle attacks, while allowing the script to authenticate the remote servers after the key rotation.

Answer

Add the -o StrictHostKeyChecking=no option to the scp command in the script.

Answer

Modify the sshd_config on each remote server to disable host key checking.

Answer

Replace scp with rsync in the script, as rsync uses a different authentication method.

Question 11

A system administrator needs to create a shell script that checks if the user 'jdoe' exists in the system and, if not, creates the user with a home directory. The script should also verify that the creation was successful. Which of the following script snippets correctly implements this logic?

Accepted Answer

if id 'jdoe' &>/dev/null; then echo 'Exists'; else useradd -m 'jdoe' && echo 'Created' || echo 'Failed'; fi. It uses `id` to check for the user's existence (redirecting output to /dev/null to suppress messages), then uses `useradd -m` to create the user with a home directory. The `&&` and `||` operators ensure that success or failure of the creation is explicitly reported, fulfilling the requirement to verify successful creation.

Answer

if grep -q '^jdoe:' /etc/passwd; then echo 'Exists'; else useradd 'jdoe' && echo 'Created'; fi

Answer

if ! id 'jdoe' &>/dev/null; then useradd -m 'jdoe'; else echo 'Exists'; fi

Answer

[ -z $(id 'jdoe' 2>/dev/null) ] && useradd -m 'jdoe' && echo 'Created'

Question 12

A developer wrote a shell script that is intended to back up log files by copying all .log files from /var/log/myapp to /backup/logs. The script runs daily via cron but the backup folder is empty. The script contains the following line: `cp /var/log/myapp/*.log /backup/logs/`. What is the most likely reason the backup fails?

Accepted Answer

No .log files exist in /var/log/myapp at the time of script execution, causing the glob to match nothing.. The glob pattern `*.log` in the `cp` command is expanded by the shell at the time the script runs. If no `.log` files exist in `/var/log/myapp` when the cron job executes, the shell passes the literal string `*.log` to `cp`, which then fails with a 'No such file or directory' error (or, depending on shell settings, may silently do nothing). This is a common issue when log rotation or cleanup removes files before the backup runs.

Answer

The PATH variable in cron is not set, so cp cannot be found.

Answer

The script does not have execute permission for the user running cron.

Answer

The cron job is not enabled because the crontab syntax is incorrect.

Question 13

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

Answer

It prints each command before execution

Answer

It enables debug mode with verbose output

Question 14

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

Answer

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

Answer

until read host; do ... done < hosts

Question 15

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=${@:-.}

Answer

dir=${0:-.}

Answer

dir=${?:-.}