University of Alaska Fairbanks
Geophysical Institute

Beyond the Mouse 2010 - The geoscientist's computational chest.

Lab 8: Unix / Shell Introduction II

Lab slides

none.

Note

As solution, send me your scripts and the answers to the questions. No datafiles please, I have plenty of those :)

Running the VirtualBox

Check here if you forgot how that works. Really. Go there if you forgot something.

Exercise 0: Permanently changing your Path and stuff

Finish last week's lab: Lab 07!

Exercise 1: Data Handling with awk

Hopefully you remember Exercise 2 of Lab 05. If not, you may remember that, at some point in the past, we had you fiddle with pesky formatting strings to extract some data from a file with a lot more data. This was Exercise 2 of Lab 05. Now we'll go back to the FAIR.pfiles text file and treat it with Unix tools to extract the information we want.

• Download the file FAIR.pfiles to somewhere in your home directory
• On the command line, extract the epoch, longitude, latitude, and height from the FAIR.pfiles file that has been passed using awk (HINT: separate variables with a comma in the print statement and they will be separated by a space in the output).
• Now figure out how to redirect this output into a new file FAIR2.llh

Now that you know how to do those two key actions, create a new tcsh script pfiles2llh in $BTM_BIN, which generalizes this for any .pfiles file it gets as a command line argument. The format for executing this script at the command line should be like this:

> pfiles2llh STATION_NAME.pfiles

Command line arguments are given to a script in various forms. ONE is using the built-in variables $0, $1 ... $N. Inside your script $0 is the program name that has been called. $1, $2, ..., $N are the first argument, 2nd, ..., n-th argument for the program that has been called. This convention is generally used when you have a few arguments that you expect to be handed to the script in a certain order. Here is an interesting article that tells you how to find the maximum number of arguments for a shell command.

Here's what your script is expected to do:

• Your script should expect ONE file to be the FIRST argument when it is called. Bonus exercise: use $# to test for the existence of an argument (i.e. give error/usage message when there is NO/too many arguments).
• extract the epoch, longitude, latitude, and height from the .pfiles file that has been passed using awk (you did this above)
• redirect the output into a new file STATION_NAME.llh:
• you will assume that a pfiles file is named following the convention STATION_NAME.pfiles
• Great, so you can extract the STATION_NAME using the program basename; save the value to a variable inside your script (e.g. sta_name)
• The output file should end up in the same directory as the input file. You can extract the path or directory name of the input file using dirname. Again, save the result to a variable in the script (e.g. sta_path).
• now redirect the output of your awk call into ${sta_path}/${sta_name}.llh
• HINT: echo the values of the variables you set for testing, to make sure you're doing things right!
• You should be able to call your script from anywhere (e.g. other scripts) having data sit any other place.
• BONUS: Allow for an optional second argument that will be the output directory (not the filename though).