Reading a File Line by Line: While Read Loop vs For Cat

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  while read host; do ... done < hosts

  Why this is correct

  Correct. The `while read host; do ... done < hosts` construct reads the file line by line, preserving each hostname exactly as it appears, avoiding word splitting and glob expansion issues.

  Related concept

  Read the scenario before looking for a memorised answer.

• ✗

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

  Why it's wrong here

  Incorrect. This approach uses a for loop that generates a sequence of line numbers using seq and wc, then reads lines with sed. It is unnecessarily complex and fragile; any change in whitespace or special characters in hostnames can cause issues. Additionally, it spawns multiple subshells and is inefficient.

• ✗

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

  Why it's wrong here

  Incorrect. Using `for host in $(cat hosts); do ... done` subjects the content to word splitting and glob expansion. If a hostname contains spaces or wildcard characters, it will be split or expanded, leading to errors.

• ✗

  until read host; do ... done < hosts

  Why it's wrong here

  Incorrect. The `until` loop is the inverse of `while`; it continues until the condition is true. The condition `read host` returns true as long as lines are read, so this loop would not execute at all because `until read host` fails immediately (read returns 0 when a line is read, so condition is false at start). Thus it never reads any lines.

Detailed technical explanation

How to think about this question

The `while read` loop uses the `read` builtin, which reads one line at a time from the redirected file descriptor, stripping trailing newlines but preserving leading whitespace and internal spaces (unless IFS is modified). This approach avoids loading the entire file into memory, making it efficient for large host lists, and it correctly handles edge cases like empty lines or lines with special characters. In real-world automation, this pattern is commonly used with SSH or Ansible ad-hoc commands to iterate over inventory files.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

• →

  Create simple shell scripts — study guide chapter

  Learn the concepts, then practise the questions

• →

  Create simple shell scripts practice questions

  Targeted practice on this topic area only

• →

  All EX200 questions

  537 questions across all exam domains

• →

  Red Hat Certified System Administrator EX200 study guide

  Full concept coverage aligned to exam objectives

• →

  EX200 practice test guide

  How to use practice tests most effectively before exam day

FAQ

Questions learners often ask

Keep practising

More EX200 practice questions

• →A system administrator needs to find all regular files larger than 10MB in /var/log. Which find command should they use?
• →A user needs to view the last 15 lines of a log file that is constantly being updated. Which command should they use?
• →Which TWO statements about systemd journal and rsyslog are correct?
• →A system administrator needs to ensure that a web server running Apache httpd starts automatically after a system reboot…
• →Refer to the exhibit. The administrator wants to create a single file system that spans the entire 20 GB disk /dev/sdb.…
• →A system administrator needs to ensure that the user 'jdoe' cannot log in via SSH but can still use other services like…