=====Practical 1: Linux Shell for Programmers=====

**Aim:** to build and install in your //home// directory a library and and application.

====Slides====

The slides for this morning's lecture on Linux are [[workshops:hpcslides|available]].

====Logging in====

Download and install putty-ssh and connect to ''lengau.chpc.ac.za'' using the username (**studentNN**) and password provided.

====Build and install zlib library====

Create a ''src'' directory to store the source.

  mkdir src
  
Copy the zlip source code tar file from my home directory.

  cp /home/student00/??? .

Fill in the ??? with the correct path and file name.

Move the tar file into the new directory:
  mv zlib-1.2.8.tar.gz src/

> Note that the version available is probably newer than 1.2.8 --- modify these instructions accordingly.

Untar the file

  cd src
  tar zxvf zlib-1.2.8.tar.gz

Load the correct environment variables using the tool "module":

  module load gcc/???

**Fill in the correct information for the ??? above.**

Prepare your own local directory structure:
  cd ~
  mkdir local
  cd local
  mkdir bin lib share include

Configure the compile environment:

  cd zlib-1.2.8
  ./configure --prefix=~/local

Compile zlib using the tool "make" (instructing it to install to your local directory):

  make install

Verify that everything is in ''~/local''

  ls -R ~/local
  

====Build a simple application using your own zlib====

Copy the ''zpipe.c'' file from my home directory (student00) into your ''src'' directory.

> You should be able to work out what the commands are by now

Edit the ''zpipe.c'' file to change the line that reads

  #include "zlib.h"

to

  #include "zzzlib.h"
  
and change the name of the ''zlib.h'' file in your ''~/local/include'' directory to match.

Now compile the object file (ends in ''.o''):

  gcc -c -o zpipe.o -I ~/local/include zpipe.c

This should find the ''zzzlib.h'' file without errors.

> Try the ''gcc'' command without the ''-I ~/local/include'' to what happens.

Now build the ''zpipe'' executable

  gcc -o zpipe -I ~/local/include zpipe.c -L ~/local/lib -lz

> The **order** of the command line options and arguments is important
> The commands to //link// the library file must come **after** the commands to //compile//.

  
If there are no errors and ''ls'' shows you a ''zpipe'' file (in green) you are done.

You can test the new ''zpipe'' program by compressing and then uncompessing a file.

  ./zpipe < test > test.z
  ./zpipe -d < test.z > test2
  cmp test test2

There should be no difference between ''test'' and ''test1''.

====Install zpipe====

Now it is inconvenient that you have to always be in the ''src'' directory to use ''zpipe'' or to have to always type the full path to it: ''~/src/zpipe''

Install ''zpipe'' in your local execultable tree

  cp zpipe ~/local/bin
  
To make sure that the shell can find ''zpipe'' you need to include your ''local/bin'' in the ''PATH'' environment variable:

  export PATH=~/local/bin:$PATH
  
Now you need only type ''zpipe'' to use it anywhere.

  cd
  zpipe --help

To make sure that each time you login that the ''PATH'' variable contains your ''local/bin'' directory, just add the ''export'' command to your ''.bash_profile'' file.

  nano .bash_profile
  
And add (or edit the existing line) to have:

  PATH=$HOME/local/bin:$PATH
  export PATH
 

====References====

  * ''zpipe.c'' is from [[http://zlib.net/zlib_how.html|zlib Usage Example]]
  * [[http://zlib.net/|zlib home]]