Understanding IOS command parsing: At the privileged EXEC prompt, you type the abbreviated command “sh ru” and receive “% ambiguous command” in response. What is the reason for this message?

Introduction / Context:
Cisco IOS allows command abbreviation so long as the typed prefix uniquely identifies a single command. When an abbreviation matches multiple possible commands, IOS cannot decide which one you intend and returns an ambiguity error. Understanding this behavior helps you create reliable shorthand and diagnose parser complaints quickly.

Given Data / Assumptions:

• You typed sh ru at the Router# prompt.
• The IOS parser compares your input against the command tree under show.
• At least two show subcommands begin with ru.

Concept / Approach:

Abbreviations work only if they are unambiguous. If both show running-config and another command such as show rusers or platform-specific variants exist, the prefix ru matches more than one candidate, triggering the “% ambiguous command” message. You must either type more characters (e.g., show run) or the full command.

Step-by-Step Solution:

Verification / Alternative check:

Type show ru? to see the parser’s options; the list will contain multiple entries starting with ru, confirming ambiguity.

Why Other Options Are Wrong:

Lacking parameters (A) is different from ambiguity; many show commands can run without extra parameters.

Claiming no command starts with ru (C) is false; running-config clearly does.

Wrong mode (D) is not the issue—show commands are valid at privileged EXEC.

Common Pitfalls:

Over-abbreviating on different IOS versions where command sets vary; relying on an alias from one platform that does not exist on another, causing unexpected ambiguity.

Final Answer:

There is more than one show command that starts with the letters ru.