Why Shell Scripts always require both read and execute permission?

Any program works fine in UNIX even it has only execute permission. By giving execute privilege alone for any program we make sure that, the users of this particular program has the permission to run the program but not to examine or copy or modify the code that we have written.

Shell scripts belongs to a special class of programs, which fails to execute if only execute privilege is granted on those. Why is this becasue, shell script, which acts as a UNIX command line macro facility, which helps in clubbing togther a series of commands into a single file and run them as a single program. Hence for the shell to execute this program (or commands inside the file), it need to read the file first and then execute.

So shell script always need both read and execute permissions!!