[gradsusr] bash command in gs, capture the result

[claudiomet]

Hi Users !

I need to execute a bash command inside of a grads script
the result of this bash command must be a grads script variable for
example (an stupid example):
-------------
'open file.ctl'
'set lat -30'
'set lon -69'
'set t 2'
'd t2'; tempkelvin=subwrd(result,4)
* the line below is Bash on grads script, it starts with exclamation
'!let celsius='tempkelvin'-273; echo ${celsius}'
--------------
Stupid example but, and I need to capture the ${celsius} Bash variable
for use in the grads script.
I don't know how to make it without using an intermediate text file,
the use of a text file is extremely slow for my purposes.
Best regards!