Edit with sed using capturing group of curly braces (windows) - json

Question

On Windows, I am trying to do an in-place edit of simple JSON files that are malformed. My files look like this, with first object duplicated.
{
"hello":"there"
}
{
"hello":"there"
}
My goal is to have only one object, and discard the second one. I should note that the files have linefeeds, as shown here.
End file should look like
{
"hello":"there"
}
I can match the first group using a regexp like ^({.*?}).*. This is fairly simple.
Seems like a perfect job for sed in-place editing. But apparently no matter what combination of escaping I do in sed, I can't match the brackets. I am using (GNU sed) 4.9 patch by Michael M. Builov.
Some results I get:
# as per original regexp
sed.exe -E "s,^({.*?}).*,d,g" double.json
-> -e expression #1, char 16: Invalid preceding regular expression
# trying to escape paranthesis
sed.exe -E "s,^\({.*?}\).*,d,g" double.json
-> -e expression #1, char 18: Invalid content of \{\}
# escaping curly brackets
sed.exe -E "s,^\(\{.*?\}\).*,d,g" double.json
-> Works, but original file is returned (no match)
Is it possible at all on Windows ? According to this and this comment it seems that Windows for some reason does not like curly brackets with sed.
Note: tested in WSL/Ubuntu, and got same result.

Answer 1

You can try this GNU sed
$ sed -Ez 's/((\{[^}]*}).*)\2/\1/' input_file
{
"hello":"there"
}

Answer 2

jq command line tool is handy to use for JSON values, even on Windows. You can download by this link as an example.
Then save the command
inputs
into a file called double.jq, and then call from command line by
[Windows key]+ cmd
cd to_the_path_where_the_files_reside
jq -f double.jq <double.json
if there are more than two independent objects within the file double.json such as
{
"hello":"there"
}
{
"hello":"there"
}
{
"hello":"there"
}
{
"hello":"there"
}
and want to pick the first one only, then convert code of the double.jq to
[inputs] | unique | .[]