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# 4 Installation

### Sections

1. Getting and installing KASH
2. Installing this package
3. Adjust the path of the executable for KASH
4. How to write a shell script which executes KASH
5. Loading and testing the package

This package provides an interface between GAP 4 and KANT respectively KASH, the shell of the computational algebraic number theory system KANT. By now the interface can only be used on a Linux system. KASH itself is not part of this package. It has to be obtained and installed independently of this package. Alnuth works with KASH version 2.4 or higher.

## 4.1 Getting and installing KASH

KASH is available at

                www.math.tu-berlin.de/~kant/download.html

Note that you have to download two files for a complete installation of KASH. For the installation of version 2.5 of KASH on a Linux system you would do the following steps:

1.
  Download the files kash_2.5.common.tar.gz and kash_2.5.3.linux.tar.gz into the same directory on your system.

2.
  Unpack the files using tar. This will create a directory KASH_2.5 containing among other files the KASH executable called kash.

The place where KASH is located in your system is independent of the place where the Alnuth-package is installed.

## 4.2 Installing this package

This package is available at

               www.icm.tu-bs.de/ag_algebra/software/assmann/Alnuth

in form of a gzipped tar-archive or as an uncompressed tar-archive.

There are two ways of installing the package. If you have permission to add files to the installation of GAP 4 on your system you may install the Alnuth-package into the pkg subdirectory of the GAP installation tree. If you do not have the permission to do that you may install the Alnuth-package in your private area. In the latter case you need to have a directory named pkg in your private area (for details see Installing a GAP Package in the reference manual).

Now move the alnuth.tar.gz of alnuth.tar file into the directory pkg and unpack it:

        bash> tar xfz alnuth.tar.gz        # for the gzipped tar-archive
        bash> tar xf alnuth.tar         # for the uncompressed tar-archive

## 4.3 Adjust the path of the executable for KASH

This package needs to know where the executable for KASH is. In the default setting Alnuth will check if there is an executable called `kash` in your search path (The search path is the set of directories through which your shell looks for executable programs when no absolute path is given. Type `echo $PATH` in your terminal to see which directories are contained in your search path.).

In Section How to write a shell script which executes KASH we explain how to write a very short shell script, which executes KASH, and indicate how you can assure that Alnuth finds it in the default setting. We recommend to use this default setting. An advantage of this method is, that in case of an installation of a new version of Alnuth you do not have to adjust the path to the executable of KASH again.

If you do not want to use the default setting, then there are two other possibilities.

If you are able to edit the file `pkg/alnuth/defs.g`, then you can change the line

        BindGlobal( "KANTEXEC", Filename( DirectoriesSystemPrograms( ), "kash" ) );

to something like

        BindGlobal( "KANTEXEC", "mykash/kash -l mykash/lib" );

where `mykash` needs to be replaced with the directory where KASH was installed. For example `mykash` could be replaced by `/usr/local/KASH_2.5`. Please note that in case of a new installation of Alnuth you will have to edit the file `pkg/alnuth/defs.g` again. Alternatively you can also change your personal `.gaprc` file (see 3.4 The .gaprc file) for setting the variable KANTEXEC to a proper value. To do this add the command line mentioned above to `.gaprc`.

The third possibility is to change the path to the executable within GAP using one of the following two functions. To do this you first have to load the package (see Section Loading and testing the package).

- `SetKantExecutable(` path`)`

  adjusts the global variable `KANTEXEC` for the current GAP session. Depending on your installation of KASH the string path has to be either the command to start KASH in a terminal (for example `kash`) or the complete path to the executable of KASH (for example `/usr/local/KASH_2.5/kash`). In the latter case the library-path does not have to be specified, but is added automatically. Thereby the message

          kash: hmm, I cannot find 'lib/init.g', maybe use option '-l <libname>'?

  will appear on the screen, which can be ignored.

  To use

- `SetKantExecutablePermanently(` path`)`

  you need to be allowed to overwrite the file `pkg/alnuth/defs.g`. The function does the same as `SetKantExecutable` and changes the file `pkg/alnuth/defs.g` respectively in addition. Thus the value of the global variable `KANTEXEC` is changed permanently. In case of a new installation of Alnuth, you will have to run this command again.

  Both functions run a test whether path is a valid string for a filename of an executable for KASH version 2.4 or higher.

  If you want to set the path to the executable of KASH using the function `SetKantExecutable` every time you start GAP, you could add the command line `SetKantExecutable(` path`)` to your personal `.gaprc` file (see Section The .gaprc file in the GAP Reference manual).

  ## 4.4 How to write a shell script which executes KASH

  In this section we explain how to write a shell script which executes KASH. Such a script is needed if you want to use the default setting of Alnuth for the execution of KASH (see Section Adjust the path of the executable for KASH).

  Switch to your home directory (`cd` ) and check (using `ls`) if there is a directory called `bin`. If not then create one with `mkdir bin`. Change to the `bin` directory (`cd bin`) and and open an empty file called `kash` with an editor of your choice. Add the lines

           #!/bin/sh
           mykash/kash -l mykash/lib

  where `mykash` needs to be replaced with the directory where KASH was installed. After this your file could look for example like this:

           #!/bin/sh
           /usr/local/KASH_2.5/kash -l /usr/local/KASH_2.5/lib

  Save the file and close the editor. Then type `chmod u+x kash` in your terminal to make the script executable.

  Now we have to assure that the directory `bin` is in your search path. Type `echo $PATH` to check if this is the case. If not then you can add `bin` to the search path by typing

          bash> export PATH=$PATH:/home/user/bin

  where `/home/user` needs to be replaced by your home directory. If you want to extend your search path permanently you can add this line to the `.bashrc` file in your home directory.

  If you use a c-shell instead of bash, then you have to extend the search path with the command

           set PATH = ( $PATH /home/user/bin )

  and edit the file `.cshrc`.

  ## 4.5 Loading and testing the package

  To use this package you have to request it explicitly. This is done by calling

          gap> LoadingPackage("alnuth");
          Loading Alnuth 1.0 ...
          true
          gap>

  Once the package is loaded, it is possible to check the correct installation by running the test suite of the package with the command

          gap> ReadPackage( "alnuth", "tst/testall.g" );

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