Experimental Physics and
Industrial Control System

"Layne \(US\), William C via Tech-talk" <tech-talk at aps.anl.gov> · Fri, 16 Apr 2021 17:24:48 +0000

Just to chime in with a bash function I tend to copy-paste for different scripts. It should work for most PVs with a string representation. (Thanks Ben for the while loop trick! I had to go update mine. It's much cleaner now!)

```sh
function monitor_pv_for_value() 
{
	# Function: monitor_pv_for_value
	# Description: Template function that executes something when monitored PV matches expected value
	# Argument 1: PV name
	# Argument 2: Expected value

	SEP="$(echo -e "\037")" 		# Field seperator for camonitor

	[ -z "$1" ] && echo "Error: arg 1 must be a PV name" && return 1
	[ -z "$2" ] && echo "Error: arg 2 must be value to watch for" && return 2

	PV="${1}"				# Removes single quote characters as the script quotes them itself
	EXPECTED_VAL="$2"

	camonitor -t n "$PV" -F "$SEP" | while read line
	do
		VAL="$(echo -ne "$line" | cut -d "$SEP" -f 3)"

		if [[ "${VAL}" == "${EXPECTED_VAL}" ]]
		then
			# Do something with matching value...
			echo "VALUES MATCH"
		fi
	done
}
```

-----Original Message-----
From: Tech-talk [mailto:tech-talk-bounces at aps.anl.gov] On Behalf Of Ben
Franksen via Tech-talk
Sent: Friday, April 16, 2021 4:38 AM
To: Johnson, Andrew N. <anj at anl.gov>; Manoussakis, Adamandios
<manoussakis1 at llnl.gov>
Cc: EPICS tech-talk <tech-talk at aps.anl.gov>
Subject: Re: Python Script call from Button press, module not found

Am 15.04.21 um 18:46 schrieb Johnson, Andrew N. via Tech-talk:
> On Apr 15, 2021, at 11:26 AM, Manoussakis, Adamandios 
> <manoussakis1 at llnl.gov> wrote:
>> I was looking mostly into the epics.camonitor or the auto_monitor 
>> parameter (seems like camonitor just when you create the pv you can 
>> set this?) in pyepics.  The python script is just a small file 
>> generator that does some basic calculations.  I was trying to have 
>> CSS just call it to run to avoid having another application to deal 
>> with.  Either by pressing a button (execute command works fine but 
>> cannot get the execute to trigger based off a rule that I know
>> of) or by a pv changing value and css calling the script (jython 
>> doesn't work with numpy/pandas).
> 
> You might want to take a look at the separate Kryten program available 
> from https://github.com/andrewstarritt/kryten which can monitor PVs 
> and run specified commands or scripts on conditions related to those 
> PVs. Since this wouldn't be running inside your GUI it isn't subject 
> to the problems related to running multiple instances which Michael 
> mentioned.
I recently had a case where I needed that functionality for a simple test
script. I resorted to plain shell scripting, see below. As written the code
works only for a single PV but I guess it wouldn't be hard to add some
filtering / case distinctions in the loop body in case you need to monitor
more PVs.

```
sel=0
caput BPMMUXCB:sel $sel
camonitor -t n BPMMUXCB:st | while read line; do
  st=$(echo -n "$line"|cut -b 33-)
  echo "st=$st"
  if test $sel = $st; then
    sel=$(( ($st + 1) % 32 ))
    caput BPMMUXCB:sel $sel >/dev/null
    echo "sel=$sel"
  fi
done
```

Ben
--
I would rather have questions that cannot be answered, than answers that
cannot be questioned.  -- Richard Feynman

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System