LFCS Question #808: Real Exam Question with Answer & Explanation

Question

Which of the following shell redirections will write standard output and standard error output to a file named filename?

Options

• A2>&1 >filename
• B>filename 2>&1
• C1>&2>filename
• D>>filename
• E1&2>filename

Explanation

This question assesses the correct syntax for redirecting both standard output (stdout) and standard error (stderr) to the same file in a Bash shell.

Common mistakes.

• A. 2>&1 >filename is incorrect because 2>&1 redirects stderr to where stdout currently points (the terminal), and then >filename redirects only stdout to 'filename', leaving stderr going to the terminal.
• C. 1>&2>filename is incorrect syntax; 1>&2 would redirect stdout to stderr, and then >filename would attempt to redirect stdout (which is now linked to stderr) to the file, but the original stderr would still go to the terminal.
• D. >>filename redirects only standard output to 'filename' in append mode, it does not redirect standard error.
• E. 1&2>filename is incorrect syntax and does not achieve the desired redirection for both streams.

Concept tested. Bash stdout and stderr redirection

Reference. https://www.gnu.org/software/bash/manual/bash.html#Redirections

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