- A
Use 'stdbuf -i0' before the script invocation to set stdin unbuffered
Why wrong: This modifies buffering but does not change the input source; stdin is still connected to the pipe, so read will not wait for user input.
- B
Use 'exec < /dev/tty' at the start of the script
Why wrong: While this redirects the script's stdin to the terminal, it permanently changes stdin for the entire script, which may disrupt other commands that expect piped input. The more targeted approach is to redirect only the read command.
- C
Use 'read input < /dev/tty' instead of just 'read input'
Correct. By redirecting the read command specifically to /dev/tty, it reads directly from the terminal, bypassing the piped stdin and ensuring the script waits for actual user input.
- D
Use 'read -t 0 input' to force immediate read
Why wrong: This sets a timeout of 0, causing read to immediately return without waiting for input, which is the opposite of what is needed.
Reading Terminal Input in Piped Scripts: Using /dev/tty
This EX200 practice question tests your understanding of create simple shell scripts. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Use 'read input < /dev/tty' instead of just 'read input'
Option C is correct because when a script is piped, its stdin is connected to the previous command's stdout, not the terminal. Using `read input < /dev/tty` explicitly redirects the read command to read from the terminal device, bypassing the piped stdin and ensuring the script waits for actual user input.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use 'stdbuf -i0' before the script invocation to set stdin unbuffered
Why it's wrong here
This modifies buffering but does not change the input source; stdin is still connected to the pipe, so read will not wait for user input.
- ✗
Use 'exec < /dev/tty' at the start of the script
Why it's wrong here
While this redirects the script's stdin to the terminal, it permanently changes stdin for the entire script, which may disrupt other commands that expect piped input. The more targeted approach is to redirect only the read command.
- ✓
Use 'read input < /dev/tty' instead of just 'read input'
Why this is correct
Correct. By redirecting the read command specifically to /dev/tty, it reads directly from the terminal, bypassing the piped stdin and ensuring the script waits for actual user input.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use 'read -t 0 input' to force immediate read
Why it's wrong here
This sets a timeout of 0, causing read to immediately return without waiting for input, which is the opposite of what is needed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Red Hat exams often test the distinction between modifying input buffering versus changing the input source; candidates mistakenly think `stdbuf` or timeout options can force terminal interaction, but only explicit redirection to `/dev/tty` ensures the read command reads from the actual terminal.
Trap categories for this question
Command / output trap
While this redirects the script's stdin to the terminal, it permanently changes stdin for the entire script, which may disrupt other commands that expect piped input. The more targeted approach is to redirect only the read command.
Detailed technical explanation
How to think about this question
In Unix pipelines, stdin is inherited from the parent process; when a script is piped, its file descriptor 0 (stdin) points to the read end of a pipe, not the terminal. The `/dev/tty` device is a special file that always refers to the controlling terminal of the current process group, allowing direct interaction with the user even when stdin is redirected. This technique is commonly used in scripts that need to prompt for passwords or confirmations while processing piped data.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the EX200 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this EX200 question test?
Create simple shell scripts — This question tests Create simple shell scripts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use 'read input < /dev/tty' instead of just 'read input' — Option C is correct because when a script is piped, its stdin is connected to the previous command's stdout, not the terminal. Using `read input < /dev/tty` explicitly redirects the read command to read from the terminal device, bypassing the piped stdin and ensuring the script waits for actual user input.
What should I do if I get this EX200 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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