amleczko is right: you should use the new library feature in Google Apps script.
However, as of today, you won't be able to do exactly what you want (using the same script for several spreadsheets). What you can do instead is save a version of your script (Files > Manage Versions...), in order to create a library. Then, import this library in the other spreadsheets (Resources > Manage Libraries...). Switch on the "development mode" so every change made do the library will immediately take affect in the spreadsheets using this library. Otherwise, you will have to save a new version of the library for every change, and manually update the version number of the library in every spreadsheets using it.
The problem is, you need to write a script in every spreadsheets using your library, with skeleton functions like this:
function doSomething(){
myLibrary.doSomething();
}
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…