CompTIA Linux+ Powered by LPI (LX0-103) — Question 18

When running the command -
sed -e "s/a/b/" /tmp/file >/tmp/file
while /tmp/file contains data, why is /tmp/file empty afterwards?

Answer options

• A. The file order is incorrect. The destination file must be mentioned before the command to ensure redirection.
• B. The command sed did not match anything in that file therefore the output is empty.
• C. When the shell establishes the redirection it overwrites the target file before the redirected command starts and opens it for reading.
• D. Redirection for shell commands do not work using the > character. It only works using the | character instead.

Correct answer: C

Explanation

The correct answer is C because when the shell processes the redirection, it truncates the target file before executing the 'sed' command, leading to an empty file. Options A and D are incorrect as they misrepresent how redirection works, while B is wrong because the command does not need to match anything to cause the file to be empty; the redirection itself is the issue.