Environment options

Environment options

Before options on the command line are processed, initial option values are set from the environment. On Windows 95/NT, these settings are added to the registry during setup. On other systems, the initial settings are determined by the HUGSFLAGS environment variable. The syntax used in this case is the same as on the command line: options are single letters, preceeded by + or -, and sometimes followed by a value. Option settings are separated by spaces; option values containing spaces are encoded using Haskell string syntax. The environment should be set up before the interpreter is used so that the search path is correctly defined to include the prelude. The built-in defaults, however, may allow Hugs to be run without any help from the environment on some systems.

It is usually more convenient to save preferred option settings in the environment rather than specifying them on the command line; they will then be used automatically each time the interpreter is started. The method for setting these options depends on the machine and operating system that you are using, and on the way that the Hugs system was installed. The following examples show some typical settings for Unix machines and PCs:

The method for setting HUGSFLAGS on a Unix machine depends on the choice of shell. For example, a C-shell user might add something like the following to their .cshrc file:
```
 set HUGSFLAGS -P/usr/Hugs/lib:/usr/Hugs/libhugs -E"vi +%d %s"
```
The P option is used to set the search path and the E is used to set the editor. The string quotes are necessary for the value of the E option becauses it contains spaces. The setting for the path assumes that the system has been installed in /usr/local/Hugs and will need to be modified accordingly if a different directory was chosen. The editor specified here is vi, which allows the user to specify a startup line number by preceding it with a + character. The settings are easily changed to accommodate other editors.
If you are installing Hugs for the benefit of several different users, then you should probably use a script file that sets appropriate values for the environment variables, and then invokes the interpreter:
```
 #!/bin/sh

 HUGSFLAGS=/usr/Hugs/lib:/usr/Hugs/libhugs -E"vi +%d %s" +s

 export HUGSFLAGS

 exec /usr/local/bin/hugs $*
```
One advantage of this approach is that individual users do not have to worry about setting the environment variables themselves. In addition to the E and P options, other options---such as +s in this example---can be set. It is easy for more advanced users to copy and customize a script like this to suit their own needs.
Users of DOS or Windows 3.1 might add the following line to autoexec.bat:
```
 set HUGSFLAGS=-P\hugs\lib;\hugs\libhugs -E"vi +%%d %%s"
```
The setting for the path assumes that the system has been installed in a top-level hugs directory, and will need to be modified accordingly if a different directory was chosen. In a similar way, the setting for the editor will only work if you have installed the editor program, in this case vi, that it refers to.
On Windows 95/NT, the setup program initializes the environment, and this can be changed subsequently (on these systems only) by using either the :set command or a registry editor. The InstallShield script that performs the installation initializes the path using the installation directory; other directories can be added using -P. Installed options are stored under the HKEY_LOCAL_MACHINE key; changes to these options using :set are placed under HKEY_CURRENT_USER so that different users do not alter each other's options.

For completeness, we should also mention the other environment variables that are used by Hugs:

The SHELL variable on a Unix machine, or the COMSPEC variable on a DOS machine, determines which shell is used by the :! command.
The EDITOR variable is used to try and locate an editor if no editor option has been set. Note, however, that this variable does not normally provide the extra information that is needed to be able to start the editor at a specific line in the input file.