Batch Sequential Processing of a List

By repetitively processing and stripping the first line in a list, the entire list can be processed. 

This is the "pure" way to use DOS to process an entire list. Very disk-intensive. Create a line fragment and put it at the head of your data file. The line fragment will be the name of your processing batch file followed by a single space. Now your data file is a batch file! After running it, you will have processed your first data line. Now run the data / batch file through FIND to strip off the first line, turning it back into a (smaller) data file again. Then add your line fragment again (turning it back into a batch file) and re-run it, this time processing the second line. Keep doing this until all lines are processed. As an example, suppose we start with this:

@echo off
type DATA.BAT | find /v /i "PROCESS.BAT" > DATA.TXT
dir DATA.TXT | find " 0 bytes" > NUL
if errorlevel 1 goto START
echo Processing %1

The "fragment.txt" has a space at the end of the word, but no carriage-return. For example "PROCESS.BAT " (but without the quotes). You'll see later why it's needed.

The "data.txt" is your data! Keep in mind, this data file will be trashed by the batch file. You may want to copy your real data source into the "data.txt" file by sticking a copy command in the "main.bat" file between the "@echo off" line and the ":START" line. Or copy it by a separate process before running the "main.bat" batch file.

The "process.bat" is the file you'll put most of your effort into. It will be called several times, getting an entire line of "data.txt" passed as an argument. It will be up to you to something more productive than simply echoing the value to the screen like I'm doing!

Here are the tricks in "main.bat". First off, everything gets redirected into NUL to keep the screen clean. The initial COPY command will result in a "data.bat" file that looks like this:

The space separating PROCESS.BAT from data1 is because of the space in the original "fragment.txt". Now you see why it's needed!

When the DATA.BAT we just created is CALLed, it will in turn run PROCESS.BAT, passing "data1" as the argument. PROCESS.BAT, in turn, will display "Processing data1" on the screen. Because DATA.BAT "runs" PROCESS.BAT (instead of CALLing it), control will *not* return to the second line of DATA.BAT after PROCESS.BAT finishes. Instead, control passes back to MAIN.BAT. Maybe it's a bit confusing about the difference between using "call" or just running a batch file, but be happy that there is a difference! That difference is what makes list processing under Win9x possible.

Next, DATA.BAT is TYPEd through FIND to remove the first line. We now have a DATA.TXT without the first line:
After removing the first line and creating a new "data.txt", we use the DIR command to see if anything is in the "data.txt" file. If we can't find the phrase " 0 bytes", then we have more data to process and we start over. If we do find the phrase " 0 bytes", then we quit.

If FIND can't find the phrase, it returns an errorlevel of one. If it does find the phrase, it returns an errorlevel of zero. Using errorlevel testing is confusing because errorlevel tests are always "greater than or equal to", so a test for errorlevel zero will always be true. Because, you know, everything is greater than or equal to zero! Practically speaking, you use "if errorlevel 1" to test for an error and "if not errorlevel 1" to test for no error.

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