PLBLinux Search Paths
Sunbelt's implementation supports a feature that is different from most programming language environments and even some PL/B implementations. The ability to specify one or more directories as `Logged on Drives' is a useful technique for organizing programs and data files into individual areas without impeding a program's ability to access them generically. If a search of the current directory fails on a generic OPEN, PREP, or CHAIN instruction, any Search Paths are also be searched in the order they are listed. By establishing a PLB_PATH environment variable, one or more directories, separated by colons, can be specified as Search Paths. Assume the following was added to the user's profile script (.profile):
and the current directory is /usr/test. In this case, the Logged on Drives would be the current directory (/usr/test) plus those in PLB_PATH (/usr/prog, /usr/txt and /usr/ndx). Therefore, the following examples would perform as described:
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An attempt would be made to OPEN the file "test.txt" within the current directory. If unsuccessful, the OPEN would then check the first directory specified in PLB_PATH. If that proves unsuccessful, then the second directory specified would be checked, followed by the third and so on until either the file OPEN was successful or the PLB_PATH list is exhausted, at which time an IO error (I03) would occur if the file could not be found.
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The guidelines listed above apply except that if "test.txt" did not exist in either the current directory or any of those in the PLB_PATH list, the file would be created within the current directory.
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An attempt would be made to locate and CHAIN to the file "test.plc" in the current directory. If unsuccessful, the directories listed in PLB_PATH would be searched until either the file is found or the list is exhausted. If "test.plc" is not found in any of the directories, a CHAIN fail error (C03) occurs.
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or
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or
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The directory preceding the name is the only one searched for its existence. The current directory or those listed in PLB_PATH are ignored.
Default file and/or program extensions, as defined with for the screen definition file, are still in effect when Search Paths are used.
See Also: Compiler and Runtime Options
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