FILTER
Advanced Programmer's Command
FILTER devspec
[USING] phantom devspec
Connects a filter program to devspec which modifies or "filters" data
as it
is
read from or written to devspec.
You
can use a filter
to
change data as it passes from devspec
to
phantom devspec (and vice versa).
A filter is a program that controls the flow of data
to
or from any
device or file.
devspec is any valid, active TRSDOS device. phantom devspec is
the name of a device which
is
connected to the filter program
established
in
memory with the SET command.
You can apply
as
many filter programs
to
devspec
as
you want
to.
If
there is not any more space
in
memory for the filter connection, the
error message "No device space available" appears.
*See the SET command for more information
on
FILTEA.
Example
Suppose
you
create a filter program named CONVERT/FLT that
converts a linefeed character
to
a "null", and you establish it
in
memory with the SET library command to a device, *LF.
F I LTER *PR
US
I NG *LF
(ENTER)
filters
1/0
directed to the line printer through the CONVERT/FLT
program.
As
a result of this filter program,
all
linefeed characters
in
output directed to the printer are converted to the null character
(ASCII
0).
Sample Use
You can use a filter to control a printer working with non-standard size
paper (see Appendix I and the FORMS library command).
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