Reading input lines without alteration | LPIC-1 102-500 Exam original practice question

105.2Standard

Read standard input one line at a time while preserving leading and trailing spaces and backslashes.

Which while condition is appropriate?

Hint 1: Focus on the requirement

Identify what must change and what must remain unchanged. Then choose the command whose scope matches that requirement.

Hint 2: Check each command's role

Separate commands that display information, change state, remove data, or affect a child process.

while IFS= read -r line; do process "$line"; done: Correct. Empty IFS and -r preserve the line content while it is read.
while read line; do process $line; done: Incorrect. Default read processing and unquoted expansion can change whitespace and boundaries.
for line in $(cat); do process "$line"; done: Incorrect. Command substitution and word splitting iterate over words rather than original lines.
read -a line | while line; do process; done: Incorrect. This is not a valid loop that reads lines.

Detailed explanation

Correctwhile IFS= read -r line; do process "$line"; done

Correct. Empty IFS and -r preserve the line content while it is read.

Incorrectwhile read line; do process $line; done

Incorrect. Default read processing and unquoted expansion can change whitespace and boundaries.

Incorrectfor line in $(cat); do process "$line"; done

Incorrect. Command substitution and word splitting iterate over words rather than original lines.

Incorrectread -a line | while line; do process; done

Incorrect. This is not a valid loop that reads lines.

An example you can run in a temporary verification environment.

printf '  a\\b  \n' | while IFS= read -r line; do printf '<%s>\n' "$line"; done

<  a\b  >

Foundation review

Check whether the command acts on the current shell, a new process, an existing process, or a file.

Use the supplied command and compare the output with the expected result.

Question IDKP-105-630

EnvironmentGNU Bash 5.2 / 標準入力

Last technical review2026-08-13