LFCS Question #804: Real Exam Question with Answer & Explanation

Question

Which of the following commands replaces each occurrence of 'bob' in the file letter with 'Bob' and writes the result to the file newletter?

Options

• Ased '/bob/Bob' letter > newletter
• Bsed s/bob/Bob/ letter < newletter
• Csed 's/bob/Bob' letter > newletter
• Dsed 's/bob/Bob/g' letter > newletter
• Esed 's/bob, Bob/' letter > newletter

Explanation

This question tests the use of sed for global string replacement within a file and redirecting the output to a new file.

Common mistakes.

• A. sed '/bob/Bob' is an invalid sed command for substitution; it would attempt to match lines containing 'bob' and then interpret 'Bob' as another command.
• B. sed s/bob/Bob/ is missing single quotes around the sed expression, and < newletter would attempt to take input from newletter, not write output to it.
• C. sed 's/bob/Bob' performs substitution only for the first occurrence of 'bob' on each line, not every occurrence as required.
• E. sed 's/bob, Bob/' is an incorrect substitution syntax, using a comma instead of the second / and lacking a replacement string after the second delimiter.

Concept tested. sed global string replacement and output redirection

Reference. https://man7.org/linux/man/man1/sed.1.html

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