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Week 47 - 2001: ls and dir
In this first week of the Java exercises I will look at the ls command
of Linux and dir command of Windows. You will implement your own version
of these commands.
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Yours first goal is to imitate the 'dir /b' from the DOS-prompt of
Windows or 'ls -1' command from Linux. (Try these out, if you are not sure
how they work.) The files of the current directory should be listed, and
only the names of the files should be shown, one file per line. Your application
do not need any input arguments. Its only function is to list all the files
of the current directory.
Hint: System.getProperty(...) and File.list()
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You have now listed the names of the files in the current directory,
and will not enhance the functionality of your application. The default
output of the “dir” and “ls” is, in addition to the name of the files,
their size and last modified date. In Linux, the owner and group are also
listed. Your task is now to imitate the command of your favourite OS.
Please be aware the owner and group of a file is not included in the
java.io.File class. Also notice that the column and row layout of both
“dir” and “ls” might be hard to implement. Do not spend too much time on
that task.
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The final small task of this week is to combine the two above. Your
application should be able to output the bare format of exercise 1 and
the full information shown in 2, thus you will type “java ls” or “java
ls –1” to choose format. To achieve this you need to implement parameter
checking.
Hints: The parameters after “ls” on the command line are passed
to the main method of your class. Thus you need to compare the String array
of main to the allowed option(s) of your application.
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If you feel ambitious this week, you could further enhance your application
by adding more parameters. Please refer to the “dir /?” or “man ls” for
information on legal options. You could also add the filter feature, by
allowing only selected files to be shown. This would allow a syntax like
“java ls ls.class” or “java ls *.java”. Refer to the Java API for which
methods of File to use.
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