I have troubles with whitespaces and command substitution. I made a tiny script to show the problem:
#! /bin/bash
a="toilet -t --font='Dot Matrix' --filter metal --filter border ABC"
#a="find . -type f -name \"hello world\""
log_error=$($a 2>&1)
if [ $? -ne 0 ]
then
echo "$a"
echo "$log_error"
exit 1
fi