Printing vectors to a file through echo command in ngspice

Hi,

I am doing a measure inside the .control statement and trying to print it out to a text file (csv to be more precise). My code inside the .control is as follows:

.control
tran 10ps 1e-08s

meas tran output_dec_0__voltage MAX v(output_dec_0_) from=8e-09s to=8.8e-09s
meas tran output_dec_1__voltage MAX v(output_dec_1_) from=8e-09s to=8.8e-09s

echo "$&output_dec_0__voltage" , "$&output_dec_0__voltage" , > report_outputs_1.csv

.endc

When I run this spice deck containing the above code, it writes out the output_dec_0__voltage and output_dec_1__voltage values to the csv file, but it writes some process id at the end of the file. The output is as follows:

1.8098 , 0.00874467, 12503 file

The "12503" is the process id and I am not sure what the "file" is.
Is there a way of disabling the process id?
Or is there a better way of writing out to the text file?

Thanks!