You must change 8080 to 8443 inside /etc/app/app.conf, saving the result in the file itself while keeping the original as app.conf.bak. Which command does that with GNU sed?
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands medium
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The options
Correct sed -i.bak 's/8080/8443/' /etc/app/app.conf
Correct. -i edits in place, and the suffix written immediately after it (no space) names the backup copy of the original.
Not correct sed -i .bak 's/8080/8443/' /etc/app/app.conf
Wrong with GNU sed. A space ends the option, so .bak is taken as the script and sed rejects it as an unknown command. This spacing is the BSD form.
Not correct sed 's/8080/8443/' /etc/app/app.conf > /etc/app/app.conf
Wrong, and destructive. The shell truncates the target before sed opens it for reading, leaving an empty file.
Not correct sed -n 's/8080/8443/p' /etc/app/app.conf
Wrong. This only prints the changed lines to standard output; the file is untouched and the unmatched lines are dropped from the output.
Why
By default sed is a filter: it reads input and writes to standard output, so the file on disk never changes. -i makes it rewrite the file in place, and an optional suffix attached directly to the option preserves the original under that name. Redirecting a command's output back onto its own input file always loses the file, because the shell performs the redirection first.
Where this comes from
- Cited
- manual page sed(1)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 103 and space the ones you get wrong.
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