SPEEDING UP BATCH FILES

 

Batch files make life a lot easier, but they are very slow.  Even when

using batch files in RAM disks, execution time is quite noticeable.  It

reminds me of the time when a batch file meant a batch of cards.  The

techniques described here reduce the time required to execute batch

file by as much as an order of magnitude.

 

Execution time is closely related to the number of lines rather than

the number of characters.  To save time put as many commands on one

line as possible.  Some ways to do this:

 

1.  Instead of using a lot of lines for remarks, put what you have to

say in a file and issue the batch command TYPE FILE.  TYPing a file

takes less than 30% as long as echoing the same information from a

batch file.

 

2.  Instead of using a lot of lines to issue commands, put all the

commands in a FOR subcommand.  For instance, your autoexec.bat file

might start out

                   fastdisk

                   parint

                   scrnsave

				   spool 7	
                   sk

                   c:

 

Instead, just say

 

    for %%f in (fastdisk parint scrnsave spool:7 sk c:) do %%f

 

This reduces six lines to one.  In Dos 2.1, but not in 3.0, you can

eliminate spaces and slightly decrease execution time like this:

 

    for %%fin(fastdisk parint scrnsave spool:7 sk c:)do%%f

 

Note the colon between spool and 7.  You can't have any spaces within

the parentheses except to denote the beginning of a new command.

 

3.  When copying files use the FOR subcommand and wild cards like this:

 

    for %%fin(print v sp)docopy a:%%f???.*

 

The FOR subcommand does not support wild cards within the parentheses.

 

How much time the FOR subcommand will save, if any, depends on how the

remembers the entire subcommand.  It doesn't have to go back to disk to

read more of the subcommand as it goes along.  But DOS doesn't remember

the contents of the batch file unless it is held in disk buffers.

Whether or not the disk buffers keep the contents of the batch file

depends on what you're doing between batch commands.

 

4.  The IF subcommand supports conditional commands and the FOR

subcommand.

For instance, you

might want to see if a file exists and, if it does, to run several

programs and then to return to the menu; or, if it doesn't to display a

message and return to the menu.

A batch file for this task might look like this:

 

         If exist myufile goto programs

         echo File does not exist.  Try again.

         d:menu

         :programs

         myprog.ram

         second.prg

         third

         d:menu

 

    If exist myfile for %%fin(myprog.ram second.prg third d:menu)do%%f

    for %%fin(echo d:menu)do%%f File does not exist.  Try again,

 

5.  When a command processor is or another batch file is invoked, batch

processing for the first batch is terminated.  You don't need to exit

the batch file.  For example, in the batch file fragment below, the

command GOTO GETOUT (and probably the label :GETOUT) is unnecessary and

will increase execution time in some cases:

            ..

         command c:

         goto to getout

            ..

            ..

         :getout.

 

6.  A fast way to get out of the middle of a batch file is to issue a

command for another batch file, say a file called exit.  EXIT can contain

only the command REM or just a dot or better yet nothing.  A file that

contains nothing doesn't take up any disk space.  You can create such a

file with another batch file, say autoexec.bat, by inserting this command

 

 

The rem part of the command can be any command that doesn't look for

parameters on the command line, e.g. cls or pause or sk.

 

7.  Of course, running batch files from a RAM disk is a big help.  It's

sometimes worth transferring control to a batch file that has been

copied onto your RAM disk.  The time required for handling the batch

operations in a RAM disk is less than a third of that required for a

floppy.

 

8.  Putting an end-of-file marker (ASCII 26 or Control Z) on the same

line and immediately after the last command, will prevent annoying

multiple prompts at the end of batch processing.

 

Bob Unferth                                           Wilmette, IL