About IDL's Path

IDL maintains a list of directories where it will search for .pro and .sav files in the system variable !PATH. If the IDL interpreter encounters a reference to a routine that is not already included in its list of compiled routines, it will search the directories specified in !PATH for a file whose name matches the referenced routine; if it finds a file with a matching name, it will compile the file and continue execution. This process is described in Automatic Compilation and Execution.

When IDL starts up, it reads the value of the IDL_PATH system preference to determine the initial value of the !PATH system variable. The value of the IDL_PATH preference is saved between IDL invocations, so changes made in one session will be present the next time IDL starts up. See IDL System Preferences for more on the preference system.

After the value of the IDL_PATH preference has been loaded into the !PATH system variable, the IDL Workbench adds entries for any open, managed projects to the end of !PATH. See Automatic Path Management for details on managed projects.

The IDL Workbench allows you to change the value of the IDL_PATH system preference using the Preferences dialog. See Paths for information on using the dialog.