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Shared Applications
BackstopBackstop is a special package installed in AFS package space that is a global catchall, designed to aid users in not being confused in using the new Isis startup script environment. Backstop is really just a script that realizes that it may have many different names, and acts differently depending on what its name is. The script also has access to a database that maps every binary installed in AFS package space to the package that holds it. Therefore if the name of the script is an arbitrary binary installed somewhere in AFS package space, it is able to tell the package in which the binary resides. For example if the backstop script thinks that its name is arc, it knows that the name of the package that arc is installed in is arcinfo. The bin subdirectory of the backstop package contains a symbolic link for every binary installed in AFS package space, each of these links points to the backstop script. This subdirectory is is placed that the end of everyuser's PATH varible in the global startup scripts. Therefore if a user tries to call a program that is not in his path (ie the user has not subscribed to the package that contains the binary or the user is on a platform that does not support the package that contains the binary), the shell will go though the PATH environment varible until it reaches the end, the bin subdirectory of the backstop package. In this directory the shell will find the program, which is actually just a link to the backstop script. When this script is executed it will print out some information about why the program is not found and offer advice to the user about how to put the program in their environment. The script is also smart enough to know that the user might have appended to PATH varible by hand, so it will check any directories listed after its own directory in the PATH varible for program. If it finds the program in one of these directories, it will execute it rather than print out its information. Effectively, what the backstop package does is replace the "command not found" error message with an error message that tells the user why the command is not found and what they can do about it. Back to the Shared Applications front page. |
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Maintained by: dci@unc.edu Url: http://help.unc.edu/dci/dci_components/sharedapps/backstop/backstop.html Last Updated: Aug 02, 1999 | |||||||||||||||||||||||||||||||||||
