EX200 Create simple shell scripts Practice Test 2 — 15 Questions

Question 1

A sysadmin creates a script to rotate log files. The script uses 'find /var/log -type f -name "*.log" -mtime +30 -exec gzip {} \;' but some log files are not compressed. The script runs as root. What is the most likely reason some files remain uncompressed?

Accepted Answer

Another process deletes log files between find's detection and execution, causing 'find' to error on missing files. Option A is correct because the 'find' command with '-exec' will fail if any file in the list is deleted (rotated) during execution, causing the whole command to produce errors and skip subsequent files. Option B is wrong because compression failure is less likely. Option C is wrong because '-mtime +30' means older than 30 days, not newer. Option D is wrong because 'gzip' handles spaces with proper quoting.

Answer

The log files are already compressed (.gz extension), and gzip fails silently

Answer

The script lacks proper quoting around {} which causes gzip to fail on files with spaces

Answer

The '-mtime +30' flag selects files newer than 30 days, so old files are excluded

Question 2

A script uses 'read' to get user input and then performs an action based on the input. However, when the script is piped (e.g., './script.sh | othercommand'), the read command does not wait for input and the script continues with empty variable. How can this be fixed?

Accepted Answer

Use 'read input < /dev/tty' instead of just 'read input'. Option B is correct because redirecting 'read' from /dev/tty forces it to read from the terminal even if stdin is a pipe. Option A is wrong because 'stdbuf' might not help with 'read'. Option C is wrong because 'read -t' sets a timeout, not a cure. Option D is wrong because changing stdin for the whole script would break piping.

Answer

Use 'stdbuf -i0' before the script invocation to set stdin unbuffered

Answer

Use 'exec < /dev/tty' at the start of the script

Answer

Use 'read -t 0 input' to force immediate read

Question 3

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. Option D is correct because 'trap - SIGINT' removes the trap and restores default behavior. Option A is wrong because 'trap : SIGINT' sets a no-op trap, not default. Option B is wrong because 'trap 2' is not valid. Option C is wrong because 'trap SIGINT' without '-' sets a trap to execute the signal name as a command, which is incorrect.

Answer

trap : SIGINT

Answer

trap 2

Answer

trap SIGINT

Question 4

Which TWO of the following are valid ways to make a shell script executable?

Accepted Answer

chmod 755 script.sh. Option A and B are correct. 'chmod +x script.sh' adds execute permission, and 'chmod 755 script.sh' sets rwxr-xr-x. Option C is wrong because '. script.sh' sources the script but does not set execute permission. Option D is wrong because 'chmod u+x' is a subset of +x but still valid; however, the question asks for two, and A and B are the most common. Option E is wrong because 'bash script.sh' runs without execute bit.

Answer

bash script.sh

Answer

. script.sh

Answer

chmod u+x script.sh

Question 5

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. Options A, B, and C are correct. A: Using 'set -e' exits on error. B: Using 'set -u' treats unset variables as errors. C: Quoting variables prevents word splitting. Option D is wrong because using 'cat' inside loops is inefficient; use I/O redirection. Option E is wrong because using 'echo' for errors is not ideal; use '>&2' to redirect to stderr.

Answer

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

Answer

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

Question 6

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. Options B and D are correct. B: A non-zero exit code indicates failure, zero success. D: 'exit 1' explicitly sets the exit code. Option A is wrong because 'exit -1' is invalid; exit codes are modulo 256. Option C is wrong because an exit code of 0 indicates success. Option E is wrong because 'exit 0' is not the default; the default is the exit code of the last command.

Answer

An exit code of 1 means success

Answer

An exit code of -1 indicates a system error

Answer

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

Question 7

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. Option C is correct because the wildcard '*.txt' only matches files in the current directory, not subdirectories. It will count lines in 'a.txt' and 'b.txt' only. Option A is wrong because it does not include backup files. Option B is wrong because it would count subdirectory files only if the glob expanded to them, which it does not. Option D is wrong because the script will run without error.

Answer

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

Answer

Line counts for .txt files in 'backup' only

Answer

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

Question 8

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. Option A is correct because $? is the exit status of the last command, which is the [[ command itself, not the command before the script. The [[ command returns 0 because the comparison is syntactically correct. Option B is wrong because $? is not the script's PID. Option C is wrong because [[ ]] does not return the negation. Option D is wrong because $? is set correctly but for the wrong command.

Answer

The [[ ]] syntax always evaluates to true

Answer

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

Answer

The $? variable always returns 0 in a conditional

Question 9

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. Option B is correct because exporting a variable in a sub-process (the script) does not affect the parent shell's environment. Option A is wrong because 'export' is used correctly syntactically. Option C is wrong because the script is executable and runs. Option D is wrong because the variable is set and exported in the script's environment.

Answer

The script lacks execute permissions

Answer

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

Answer

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

Question 10

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.. Option A is correct because wc -l output includes the filename, making $lines a string such as '45 /etc/passwd', which cannot be used in arithmetic. Option B is incorrect because -c counts characters. Option C is misleading; $((...)) works on integers. Option D is wrong because the syntax is valid.

Answer

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

Answer

The script has a syntax error in the echo command.

Answer

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

Question 11

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. Option B is correct because 'bash -n script.sh' performs syntax checking only. Option A ('set -x') enables execution trace. Option C ('bash -v') prints lines as read. Option D shows the path of bash.

Answer

which bash

Answer

set -x

Answer

bash -v script.sh

Question 12

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

Accepted Answer

read. Option B is correct because the 'read' built-in reads a line from standard input into a variable. Option A (echo) outputs, not reads. Option C (printf) formats output. Option D (cat) reads files, not user input.

Answer

printf

Answer

cat

Answer

echo

Question 13

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. Option C is correct because using IFS= and -r preserves whitespace and backslashes. Option A does not use -r, breaking backslashes. Option B splits on spaces and globs. Option D uses an invalid here-string redirection for a file.

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 14

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). Option B uses find with -type f to count files, correctly handling filenames with spaces. Option D uses find with -printf to print a character per file, then wc -c counts characters. Option A includes directories. Option C uses ls -1A which shows all entries including directories. Option E uses stat but misses hidden files due to glob * not including dot files.

Answer

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

Answer

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

Answer

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

Question 15

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.. Option A (using [[ with =~ for regex) is a bash-specific feature, but in RHEL bash is default, so it's valid and often recommended for readability. Option C (quoting variables) is a fundamental best practice to prevent word splitting. Option E (using local in functions) limits variable scope and avoids side effects. Option B (source vs .) is a matter of preference; both work. Option D (set -e) can cause unexpected exits and is not always recommended.

Answer

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

Answer

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