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September 14, 2018

Use Command Interpreter to program fast

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By Ken Robertson

An overworked, understaffed data processing department is all too common in today’s ever belt-tightening, down-sizing and de-staffing companies.

Running-shoesAn ad-hoc request may come to the harried data processing manager. She may throw her hands up in despair and say, “It can’t be done. Not within the time frame that you need it in.” Of course, every computer-literate person knows deep down in his heart that every programming request can be fulfilled, if the programmer has enough hours to code, debug, test, document and implement the new program. The informed DP manager knows that programming the Command Interpreter (CI) can sometimes reduce that time, changing the “impossible deadline” into something more achievable.

Getting Data Into and Out of Files

So you want to keep some data around for a while? Use a file! Well, you knew that already, I’ll bet. What you probably didn’t know is that you can get data into and out of files fairly easily, using IO re-direction and the print command. IO re-direction allows input or output to be directed to a file instead of to your terminal. IO re-direction uses the symbols ">", ">>" and "<". Use ">" to re-direct output to a temporary file. (You can make the file permanent if you use a file command.) Use ">>" to append output to the file. Finally, use "<" to re-direct input from a file:

echo Value 96 > myfile
echo This is the second line >> myfile
input my_var < myfile
setvar mynum_var str("!my_var",7,2)
setvar mynum_var_2 !mynum_var - (6 * 9 )
echo The answer to the meaning of life, the universe
echo and everything is !mynum_var_2.

After executing the above command file, the file Myfile will contain two lines, “Value 42” and “This is the second line.” (Without quotes, of course.) The Input command uses IO re-direction to read the first record of the file, and assigns the value to the variable my_var. The first Setvar extracts the number from the middle of the string, and proceeds to use the value in an important calculation in the next line.

How can you assign the data in the second and consequent lines of a file to variables? You use the Print command to select the record that you want from the file, sending the output to a new file:

print myfile;start=2;end=2 > myfile2

You can then use the Input command to extract the string from the second file.

Rolling Your Own System Variables

It’s easy enough to create a static file of Setvar commands that gets invoked at logon time, and it’s not difficult to modify the file programmatically. For example, let’s say that you would like to remember a particular variable from session to session, such as the name of your favorite printer. You can name the file that contains the Setvars, Mygvars. It will contain the line: setvar my_printer “biglaser”

The value of this variable may change during your session, but you may want to keep it for the next time that you log on. To do this, you must replace your normal logoff procedure (the Bye or Exit command) with a command file that saves the variable in a file, and then logs you off.

byebye
purge mygvars > $null
file mygvars;save
echo setvar my_printer "!my_printer" > *mygvars
bye

Whenever you type byebye, the setvar command is written to Mygvars and you are then logged off. The default close disposition of an IO re-direction file is TEMP, which is why you have to specify a file equation. Because you are never certain that this file exists beforehand, doing a Purge ensures that it does not.

07:14 PM in Hidden Value, Homesteading | Permalink

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