Which command can verify a program's installation and locate its path (for example under /usr/local/bin)?

• A. which PROGRAMNAME
• B. whereis PROGRAMNAME
• C. command -v PROGRAMNAME
• D. type PROGRAMNAME

Answer: (D)

The command that best serves this need is about how the shell resolves a command name. The built-in that does this shows you exactly how the shell would run the program and where its executable lives. It tells you whether the entry is a shell builtin, a function, an alias, or an external program, and, if it's external, prints the full path to the executable (for example, /usr/local/bin/PROGRAMNAME). It also accounts for hashing or previous resolutions, so you get the true location the shell will use. If the command isn’t available, it clearly indicates that, confirming whether it’s installed or not in the current PATH.

Other utilities have drawbacks for this use case. Which only locates external commands in PATH and doesn’t reveal aliases, functions, or builtins. Whereis searches common locations but isn’t precise about which one the shell will actually execute and can return multiple results. command -v is portable and can show a path, but it offers less contextual detail about the command’s nature and behavior in the shell.