variable input to ALSA via .asoundrc + shell variable

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Hello.

It came to my attention, that I can start process and pass some
variable to ALSA upon execution, so it may change PCM for example.

I took information from here:

http://blog.vrplumber.com/b/2012/03/23/control-default-alsa-device/

I tried it and it worked. However, it didn't work as expected for me. I
was able to see rate is changing if I used various PCM with variable.
So this part worked.

I was able to check with /proc/asound/card0/pcm0p/sub0/hw_params file,
it showed correct rate when I was using different PCM's.

However, it seems that something happened to dmix,
Some processes failed with "device busy" message, devices, who used
default rate settings, to which I did not change rate with shell
variable.

My question, is, is there any user documentation to those three lines:
@func getenv
 vars [ DISPLAY_ALSA_DEVICE ]
 default front

I get that "default" tells !default PCM to use "front" in case shell
variable "DISPLAY_ALSA_DEVICE" is empty or doesn't correspond to
existin PCM.
I need to know, "@func getenv", how it works.
I want to know if function in question can be used in non !default
device? My testing showed, that it's not, but may be I am not doing
something right. In other words, if shell variable can be read by
different PCm than "!default"?

I have read ALSA programmer's documentation on this function,but words
are so generic, that I(no programmer) didn't understand them.

Thanks in advance
Dmitri Seletski

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