Gfilui

What is the difference between installing an application software and copying the executable file(ex:a.out) of the application? When we run the a.out file it gives some result, running the application that is installed also gives some result. I don't understand the difference when some one says "Installing an application", and copying an executable file. What actually happens when an application is installed? How is it different from just copying the executable from one computer to another(same os and similar hardware) and running it there?

Well, when saying installing an application, that normally means that you use a package manager like dpkg or the higher level apt family. In this case, the executables are shipped in a package that also can contain additional libraries that are needed to run the executable, manpages, developer files, configuration files etc. The advantage of this is that the admin can keep track of what is installed and also ensures that when installing new software or updates, the new software does not clash with other software and libraries already installed which could lead to other applications crash.

So, while it might work to just copy over your executable to another system, it is not recommended as it can break things. It is safe to copy executables to somewhere outside the system paths like /bin/, /sbin, /usr/bin, /usr/sbin.

You could use /usr/local/bin and /usr/local/sbin for such a purpose or even better create a directory beneath /opt for your executable and place it there. Then call the executable with the full path or add the path to the executable to your PATH environment variable.

$ mkdir -p /opt/myapp/bin
$ cp myexec /opt/myapp/bin/

$ /opt/myapp/bin/myexec

or

$ export PATH=$PATH:/opt/myapp/bin
$ myexec

A core principle of all Unix-like operating systems (like Ubuntu) is everything is a file. If you look at the contents of a package, you will also find an executable file there, and yes, for two machines with the exact same (or at least very similar) combination of software and hardware (platform), you could just use your executable. But most programs do not consist of only one executable. Run ls -R /usr |grep libreoffice for an example of a more complex package, you wouldn't want to copy all those files in their individual locations by hand now, would you?

While in some cases (especially when testing small programs) it does make sense to just send someone an executable they can run, you will almost always want to provide a package for a finished product.

Package managers usually also take care of installing dependencies, adding your program to the list of installed applications and PATH, and last but not least provide an option to update the program when a new version is released.