CS270 - System Software
Lab Assignment #8
Spring 2021
The purpose of this assignment is to give you practice writing Perl scripts.
Many systems today provide the users with a trashcan for deleting files. Unwanted files are not
actually deleted, but rather are moved to a designated subdirectory. They still exist as regular
files until the user does an “empty trash” operation, at which time the files truly are deleted.
You are to write a Perl program, called rf (for round file), that implements the trashcan function.
When rf is invoked without any options, the specified files should be moved to a subdirec-
tory called roundfile. If roundfile does not exist, it should be created in the user’s home
directory, and a message stating that it has been created should be printed. If a directory is
specified, then the directory (along with all of its contents) should be moved. If a file specified
in the rf command has the same name as a file that already exists in roundfile (i.e., a file with
the same name has already been rf’ed), then one of two things should happen:
• If the newly deleted file’s contents are the same as the previously deleted file (as would be the
case if the same file were deleted twice), then the new file should replace the old file - that is, the
file’s date should reflect the most recent deletion.
• If the newly deleted file’s contents are different than the previously deleted file, then both files
should be kept. The newly deleted file’s name should be changed to include a “version” number.
For example if we try to delete a file named file.txt, but a file already exists with that name,
the newly deleted file should have the name file.txt.1 . If subsequently another file named
file.txt is deleted, its name should be file.txt.2, etc.
The rf command should support at least the following options:
• -e - empty the trash. All files in the roundfile directory should be (really!) deleted.
• -f - flush. Like -e, except that the roundfile directory itself should also be deleted.
• -i - interactive. The program should ask the user before rf’ing any file (similar to rm -i).
• -l - list. The files in roundfile should be listed, similar to issuing the command ls -l roundfile.
Directories should be listed, but their contents don’t need to be.
• -r - retrieve. Copy the specified file from the roundfile directory to the current directory. If a file
with the same name as the retrieved file already exists in the current directory, then your script
should ask the user if the retrieved file should replace the existing one. If the answer is ”no,”
then nothing should happen.
Your program should also accept any reasonable combination of the above options. For ex-
ample, the commands rf -i -f, rf -if and rf -fi should all work the same. All “error”
messages should be produced by your Perl script, and not from any of the system utility pro-
grams.
Submit your program using the cscheckin program.









































































学霸联盟