Here's a version of the script that works:
#!/usr/bin/env wolframscript -print All -run \'Needs[\"ComputerArithmetic`\"]\'
This is a limitation of -print All that we probably should either document or find a fix for, though the latter is rather challenging. When executing a script normally or using -print, wolframscript can essentially tell ...
You should put it in this folder:
Packages that you put there will also be automatically available when a new version of Mathematica is installed.
You can also install packages from the File menu, File -> Install. It will place the file in the same folder as mentioned above, as I recall (it's been a while....