Learn Microsoft Access Advanced Programming Techniques, Tips and Tricks.

Disk Operating System Commands in VBA

The first edition of Microsoft Disk Operating System (MS-DOS 1.0) was launched in 1982.  The first edition of Microsoft Windows 1.0 Operating System, Disk Operating system with Graphical User Interface (GUI), released on November 20, 1985 – Source: www.wikipedia.org.  The Disk operating System Version under Windows7 is 6.1.7600.

Disk Operating System Commands (both Internal and External) are directly used under Command Prompt for managing Files, Folders on Disks and for retrieving information on them.

For example, the Directory Command (Dir /S/B/P) will provide a list of all files with full Path Names (like C:\My Documents\New Folder\Resume.doc) from your C: Drive and display them on screen, one page at a time. 

Let us try an example.

Click on the Start Menu.

Type cmd and press Enter Key, DOS Command window will open up with the Command Prompt C:\>.  Type the following Command to display a list of Folders/Files from your C: drive, one page at a time.  You must press a Key to advance the list from one page to the other.

Warning:  The list of Folders/Files on your C: drive will run into hundreds of pages.  Press Ctrl+C (break the command) to terminate the list from displaying further.

C:\> Dir /S/B/P

C:\> is the command prompt

Dir (command stands for Directory)

Command switch /S includes Files in Sub-directories also in the output.

Command switch /B provides a bare-formatted list of files, i.e. gives only file path names without creation date, file sizes or any other information of files.

Command switch /P displays the output on Screen one Page (one screen full) at a time.  Needs to press a Key on the Keyboard to advance the list of files to the next Page.

If you want to save the entire list into a text file, without page breaks, issue the following command with the output redirection symbol (>) with a text file name.  The re-direction symbol will send the output of the Directory command to a specified text file, without displaying them on screen.

C:> Dir /S/B > myDirList.txt

Note: Leave a space on either side of the > symbol.

You may open myDirList.txt file in Notepad and check the contents. You can display the contents of myDirList.txt file with the following DOS Command:

C:\> TYPE myDirList.txt

Press Ctrl+C to stop the runaway display. TYPE command displays the contents of a text file on screen. But, it will not display the output one screen full at a time. To do that we can seek the help of another DOS command: MORE with the use of piping symbol (|).

C:\> TYPE myDirList.txt | MORE

In the above command we are using the piping symbol (|) to join the TYPE filename.txt | MORE commands to get the required output. The TYPE command reads the text file contents and pass it on to the next command MORE, without directly sending the output to the Screen. MORE Command takes it's input from TYPE command, through the pipe, and displays it one screen-full at a time. Press SPACEBAR to display the next screen-full of text.

OR

C:\> MORE < myDirList.txt

If > (greater than) symbol is known as re-direction symbol in DOS then < (less than) symbol is known as Source symbol for the MORE command. MORE command reads data from the file name given immediately after the Source Symbol (<) and displays one screen-full at a time.

Let us come back to the Dir Command, it is available in VBA also. But it is used for a different purpose. We can use this command to check the presence of a particular file or the presence of any file in a folder. The usage of this command is as shown below:

strOutput = Dir("C:\My Documents\Resume.doc", vbNormal)

The Dir Command checks for the presence of Word File Resume.doc in Folder C:\My Documents, if found then the file name 'Resume.doc' is returned in strOutput Variable, otherwise it will return an empty string.

strOutput = Dir("C:\My Documents\*.*", vbNormal)

This command will get the first file name and save it in strOutput Variable. You may try out this command in the Debug Window directly, like:

? Dir("C:\My Documents\*.*")

This will print the first file name found in the folder C:\My Documents in the Debug Window. To get subsequent file names from the same folder you can run the command without any parameters to the function, like:

? Dir()

Note: First time when you run this Command you should provide a Path as parameter otherwise it will end up with error.

Place the insertion point on the Dir() Command and press F1 to display the details of this Command in Access Help Documents.

There are other interesting Windows Operating System Commands like ChDrive, ChDir, MkDir, RmDir etc. and we will learn their usage in VBA Next week.

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