Convert Terraform string to multiline string

terraform-single-to-multiline-string.sh

# First iteration: convert single line strings to EOF blocks for 
# resource argument called filter.
#
# filter = "foo\nbar" 
#
# becomes 
#
# filter = <<EOF
# foo\nbar
# EOF
sed -E 's/filter[[:space:]]+= "(.*)"/filter = <<EOF\
\1\
EOF/' in.tf > out.tf

# Second iteration: replace newlines in EOF blocks to actual lines.
#
# filter = <<EOF
# foo
# bar
# EOF
sed -E ' /filter/,/EOF/ s/\\n/\
/g' out.tf > out2.tf