127 lines
5.4 KiB
Plaintext
127 lines
5.4 KiB
Plaintext
DOS Level 2:
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We have seen that DOS's mission is one of file management. Every software
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has a purpose and DOS's is for housekeeping of files. However, we also saw
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that DOS is unique because we can't run the computer without it. We must
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"boot" the system with the internal DOS files each time we start the computer.
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Finally, most people don't realize that DOS is also the Swedish word for
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toilet. Which DOS is more important in your life? Too obvious to comment.
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WHEN A COMPUTER IS POWERED-UP
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-----------------------------
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What actually happens when the computer is started? First, a factory preset
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set of instructions residing in ROM are activated. ROM stands for Read Only
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Memory. This set of chips can send instructions TO RAM, but it cannot receive
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them - thus cannot be altered. The unalterable set of ROM instructions
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performs systems checks to make sure all critical hardware components are
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hooked up properly and in the case of RAM - operating properly.
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Once the hardware check is performed, ROM instructs RAM to search the A drive
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for internal DOS files. If no disk is present in drive A, then ROM directs
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RAM to check the Root directory of the hard drive for the necessary files
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(more on Root directories in Hard Disk DOS lessons). If the files are found,
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they are automatically loaded into to RAM (booted).
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There are 3 files which comprise internal DOS: IBMDOS.SYS, IBMBIO.SYS and
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COMMAND.COM. The first 2 files are hidden files. They cannot be seen in a
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DIR command, nor can they be copied or deleted with conventional DOS commands.
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These files are responsible for the linking of the hardware components. The
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final file, COMMAND.COM CAN be seen, copied or deleted, and contains the
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frequently used internal DOS file management commands. Again, the system will
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not boot without these 3 files.
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It is from the DOS prompt: A>
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that we can go forward with
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the task of file management.
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We have already seen a handful of the most useful DOS file management
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commands. Lets expand their abilities with the use of file WILDCARDS.
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WILDCARDS
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Wildcards allow the power of a DOS command to expand. For example, imagine
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that you need to copy 12 files from a disk containing 100. The 10 files all
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begin with the word SALES. Sales.Jan, Sales.Feb, Sales.Mar ...
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We could copy each file individually: A>Copy Sales.Jan B:
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A>Copy Sales.Feb B:
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......
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Or, we could do it in one command with the use of a wildcard:
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A>Copy Sales.* B:
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The asterisk (*) represents a wildcard. It is often referred to as a star.
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The above command would read "Copy Sales dot star space B full colon".
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Any DOS command that references a filename can make use of wildcards to
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expand the command. When a Copy command is issued, DOS is instructed which
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single file to copy. However, when we use a wildcard, DOS is instructed to
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use any files that meet the criteria. The asterisk expands the criteria for
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qualifying files.
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A>Copy Sales.* B: says "copy any file from drive A to drive B that contains
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SALES as the filename, regardless of the extension"
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What if we wanted to include the files: SALES1.DOC, SALES10.DOC and
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SALESMAN.SUM
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SALES.* is not broad enough criteria to include these files. Rather, we would
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state it:
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A>Copy SALES*.* B:
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Now the criteria is to copy ANY file as long as the first 5 characters are S A
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L E S regardless of what other characters come after these first 5 in the
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filename or what exists in the extension.
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The asterisk is the broadest and most often used wildcard. Some other
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examples of its use:
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A>Copy *.DOC B: (all files with the extension DOC)
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A>Del S*.* (any file that begins with the letter S)
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A>Del B:*.* (ALL files from the B drive - be careful!)
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A>Dir B:*.COM (A list of all files with an extension of COM
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on the B drive)
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Anywhere a file specification can be given in DOS, the specification can be
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broadened with a wildcard. The asterisk is very useful.
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Another wildcard is the question mark (?). It too broadens the criteria for a
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command, however, it is "location specific". For example:
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A>Copy S?.DOC B:
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Any file that has S as the first character followed by a single character
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in the second position or not, but NO more characters in the filename plus an
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extension of DOC.
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Therefore, these files would make it: S.DOC SA.DOC SI.DOC S5.DOC.
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And, these files would not: SALES.DOC SAT.DOC S5.EXE
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Wildcards can be used together:
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A>Copy S?L*.* B:
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This will use the following: SALES.COM SAL S5L.DOC SL.EXE
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But not: SAM.DOC BUDGET.SL
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The wildcard characters, * and ? are used with DOS commands such as DIR,
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COPY and DEL to broaden their application. An asterisk, or "star" allows up
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to 8 characters at any position in a file name. A question mark does the
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same, but for only 1 character position.
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***** END OF FILE: Press <ESC> to return to Main Menu *****
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