whatis

The whatis command is used to give a brief description of what a command does.

Example

whatis whatis

This will return

whatis(1) - search the whatis database for complete words

This will actually return all word matches on 'whatis', which is more than a single line entry. To do a closer match use the cap (^) symbol at the start of the search term to do a regular expression match where the line must begin with the search term.

Example

whatis ^whatis

which

The which command is used to display the full path for the executable that is passed to it.

Example

which curl

This may return

/usr/bin/curl

whereis

The whereis command is used to display and paths to executables, sources files or manual pages connected with the command passed to it.