Try this: $ type command command is a shell builtin Respectfully-RTM (assuming bash): $ man bash It's a big manpage, so i'll spare you. command

Try this: $ type command command is a shell builtin Respectfully-RTM (assuming bash): $ man bash It's a big manpage, so i'll spare you. command [-pVv] command [arg ...] Run command with args suppressing the normal shell function lookup. Only builtin commands or commands found in the PATH are executed. If the -p option is given, the search for command is performed using a default value for PATH that is guaranteed to find all of the standard utilities. If either the -V or -v option is supplied, a description of command is printed. The -v option causes a single word indicating the command or file name used to invoke command to be displayed; the -V option produces a more verbose description. If the -V or -v option is supplied, the exit sta- tus is 0 if command was found, and 1 if not. If neither option is supplied and an error occurred or command cannot be found, the exit status is 127. Otherwise, the exit status of the command builtin is the exit status of command. 'command -v something' just tries to run the 'something' command and fails if it is not found. So, in this instance, try to run 'md5' then try to run 'md5sum'.