A typical location for programs that are accessible system-wide on most Unix-like systems is /usr/local/bin, and this directory is included in the $PATH of every user. If you want hello to be available system-wide, and you have permission to write to /usr/local/bin, you might put it there, using su or sudo to get root permissions first:
bash$ sudo -s Password: bash# mv hello /usr/local/bin
Note that for the last command line, we use bash# instead of bash$, to denote a shell that is running as the system administrative root user.
If we're able to do this, we should be able to call the hello program from anywhere on the system and as any user, just with the word hello:
bash$ hello Hello, bashuser! bash$ sudo -s Password: bash# ...
