#3 Lab Automating Installation & Introduction to Make Due in Lab, September 15, 2004
Name: Lab Time: Grade: Error Checking In this lab you will be writing a shell script to automate the installation of a system. The system that your shell script will install is the gnuchess system that you installed by hand in lab 1. Since commands are not being typed interactively by a user, a shell script needs to avoid making assumptions. Error messages generated during the execution of a shell script are likely to go unnoticed as the output scrolls quickly across the screen. The programmer of a shell script, therefore, should be aware of, and try to prevent, possible error conditions that might occur when the shell script executes. One possible source of errors is the directory structure. A shell script should avoid using non-existent directories. As such, it needs to check for the existence of any directory it intends to use, and be able to create missing directories as needed. Of course, there is a limit to how much checking a shell script can or should do. For example, shell scripts rarely need to check for the existence of a users home directory. The amount of error checking required is, therefore, a design decision that must be made by the scripts programmer. Before making this decision, the programmer should consider the scripts users. How likely are they to encounter a particular error, and will they be able to deal with it, if it is not handled by the shell script? In addition, a programmer may have external requirements imposed by a manager, or customer, specifying the type of errors that must be handled. Your shell script should not make assumptions about the existence of architecturespecic subdirectories (such as .../arch/x86/build/..., etc.) when building and installing the gnuchess program. If any required directory does not exist, your shell script needs to create it. This allows your shell script to proceed with condence in the automated installation. Automatically Setting up Your Architecture-Specic Directories 1. To congure your architecture specic directories create a shell script called archdir-setup and put it in your ~/csci3308/bin directory (recall, this is your architecture-independent bin directory). /10
1
2. This shell script should be written so that it can be run from any directory. You should either use absolute paths, or change directory so that you know where you are before using relative paths. 3. In this shell script you can assume that the directory ~/csci3308/arch exists. Add the following commands to your shell script to create the architecture specic subdirectories: #!/bin/tcsh -f cd ~/csci3308/arch/$ARCH mkdir bin build include lib man tmp 4. Make this script executable. Then type rehash. This will reset the hashtable the shell uses to optimize nding commands. Now use which or where to make sure that archdir-setup is in your path. 5. Now run the script. You should see a few error messages (up to six) as the script tries to create directories that already exist. If you do not see any error messages, then check that your $ARCH variable is dened and then run the script again. These error messages are not very serious, given our purpose for this script. We are merely double checking that these directories exist. If they already exist, thats ne. However, the user should not have to see this type of error message. 6. To avoid these error messages, rewrite your script so that it rst checks if a directory exists, and only calls mkdir if the directory doesnt exist. To do this you will need to use the if statement, and le inquiry operators. You can learn more about le inquiry operators on page 639 of the Linux Shells by Example textbook. 7. We are now going to simulate running this script on a dierent architecture. Redene your $ARCH environment variable (on some accounts, this variable is $arch) to have the value sun4: setenv ARCH sun4 or setenv arch sun4 8. Before running the script, verify that you do not have a sun4 directory in your ~/csci3308/arch directory. If you do, remove it with the command: yes | rm -r 9. ~/csci3308/arch/sun4 Now, run the archdir-setup script again. What happens?
10. While we can assume that the ~/csci3308/arch directory exists, we can not assume that a particular architecture-specic subdirectory exists. Modify your script to create the architecture-specic subdirectory, if needed. 2
11. Run your script again to make sure that it works correctly. (It should create the .../csci3308/arch/sun4 directory, and then create the bin, build, and other directories beneath it). Run the script a second time to make sure it doesnt produce error messages when the directories already exist. 12. Now, change your $ARCH variable back to its correct value: setenv ARCH x86 or setenv arch x86 13. Print out your archdir-setup script and turn it in with your lab. Writing the Installation Shell Script 14. You will now write a shell script that installs gnuchess automatically. This script will be called gnuchess-install, and it should be in your architecture-independent bin directory. In order to work, your shell script will require that the gnuchess distribution has already been downloaded and unpacked into your src directory. 15. The rst thing your shell script should do is run your archdir-setup script. This ensures that all of the directories that it needs exist. 16. Before building gnuchess your shell script needs to make a new subdirectory of the architecture-specic build directory. Add the command(s) to your shell script to create this directory, but make sure that your script will not print an error message if this directory already exists. 17. The following steps need to be taken to install gnuchess. For each step add the necessary command(s) to your gnuchess-install shell script. Look back at lab 1 to help you remember the exact commands. (a) Localizing (congure) (b) Building (make) (c) Installing (make install) 18. Now nish up your shell script by making it executable, and making sure of the following things. The shell script should be in your path, and it should work regardless of what directory you are in when you run the script, i.e., you cannot assume that you start in the build directory. 19. Test your script starting with a clean environment. Change to the directory ~/csci3308/arch/$ARCH and remove all of its subdirectories. Run your gnuchess-install program and check to see that it automatically creates the needed directories, builds gnuchess, and installs it in the correct directory. 20. Print out your gn...