The :help magic command can't find the documentation for any IDL commands!

The text version of the online help must be built specifically with the onlinehelp target:

make onlinehelp
make install

I get an error about "_ridl_preflocation = ridl_preflocation()" when I launch rIDL. What's wrong?

You might get an error like the following:

rIDL 0.2.0: Really Interactive Data Language. [Build: 08/04/2011]
IDL Version 8.1, Mac OS X (darwin x86_64 m64). (c) 2011, ITT Visual Information Solutions
Installation number: 17209.
Licensed for use by: Norut Information Technology

_ridl_preflocation = ridl_preflocation()
                                        ^
% Syntax error.
% String expression required in this context: _RIDL_PREFLOCATION.
/usr/local/bin/ridl.sh: line 21: 35954 Segmentation fault
/usr/local//bin/bin.darwin.x86_64/ridl $@

rIDL is calling the RIDL_PREFLOCATION routine found in the ridl_preflocation.pro file. To fix, simply put the share/idl directory of the rIDL installation in your IDL !path, e.g., by setting the IDL_PATH environment variable.