Exam 101-400 topic 3 question 49 discussion

Actual exam question from LPI's 101-400

Question #: 49
Topic #: 3

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

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.

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Suggested Answer: C 🗳️

by DuboisNicolasDuclair at Oct. 21, 2023, 6:48 p.m.

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DuboisNicolasDuclair

1 year, 4 months ago

Selected Answer: C

The reason `/tmp/file` is empty after running the command: C. When the shell establishes the redirection, it overwrites the target file before the redirected command starts and opens it for reading. In this scenario, the shell processes the redirection before the `sed` command is executed. As a result, the output file, `/tmp/file`, is emptied before `sed` even begins processing the data from the input file. This is why the file ends up empty.

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Exam 101-400 topic 3 question 49 discussion

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DuboisNicolasDuclair

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