EX200 Essential Tools Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  sed '/^#/!s/enabled/disabled/g' /etc/ssh/sshd_config

  Why this is correct

  The address '/^#/!' uses negated matching: sed applies the following command only to lines that do not begin with '#', i.e., active configuration directives. The s/enabled/disabled/g substitution then replaces every occurrence of 'enabled' with 'disabled' on those lines, with the g flag ensuring all matches per line, not just the first. Because sed's default action prints every input line, the output stream contains the complete updated file, and comment lines remain untouched as required.

• ✗

  sed 's/enabled/disabled/g' /etc/ssh/sshd_config

  Why it's wrong here

  Without an address restriction, the s/// command is applied to every line of /etc/ssh/sshd_config, including lines that start with '#'. This is problematic because comments frequently contain the word 'enabled' in examples or explanatory text, so those comments get silently modified when they should remain as documentation. The g flag makes the unwanted replacement exhaustive even on comment lines, and since sed writes to standard output by default, the configuration file itself is never changed.

• ✗

  sed -n '/^#/!s/enabled/disabled/gp' /etc/ssh/sshd_config

  Why it's wrong here

  While '/^#/!' correctly excludes comment lines, the -n flag suppresses sed's default automatic printing of every line, and the trailing p flag prints only lines that actually underwent the substitution. As a result, the command produces a partial output stream consisting solely of modified non-comment lines, omitting comments and unchanged directives entirely. That output goes to stdout rather than back into the file, so the administrator never writes changes to /etc/ssh/sshd_config and cannot rely on this as an edit operation.

• ✗

  sed '/^#/s/enabled/disabled/g' /etc/ssh/sshd_config

  Why it's wrong here

  This command inverts the required selection by using '/^#/' as the address, which matches only lines that begin with a comment marker and applies the substitution exclusively to those lines. Consequently, active directives that should be changed are never touched because they do not start with '#', leaving every 'enabled' in the real configuration intact. Additionally, comment lines may get mangled as 'enabled' is replaced with 'disabled' in documentation, further corrupting the intended file with unwanted changes.

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