Sed don't work with a special variable - json

Question

I have a command that adds to a specific location of the file.
a="hellotesting"
sed "/^[[:blank:]]*\"testing_$2\": \[$/,/^[[:blank:]]*],*$/ {s/^[[:blank:]]*}$/&`echo $a`/}" $1
It's work ! Output (is a JSON file and i don't want to use jq)
{
"mytable_test": [
{
"test1": "abc",
"test2": "def",
"test2": "ghi"
}hellotesting
],
"mytable": [
"test1",
"test2",
"test3"
]
}
But I can't put the contents of a file.
My file:
yeah
is
test
my
script
And in my program:
IFS=
a=$(cat file)
sed "/^[[:blank:]]*\"data_$2\": \[$/,/^[[:blank:]]*],*$/ {s/^[[:blank:]]*}$/&`echo $a`/}" $1
I have an error:
sed: -e expression #1, char 73: unterminated `s' command
I want this output:
{
"mytable_test": [
{
"test1": "abc",
"test2": "def",
"test2": "ghi"
}yeah
is
test
my
script
],
"mytable": [
"test1",
"test2",
"test3"
]
}
But, if my file is just:
yeah
And I cat file in my variable, that work ..
I don't understand ..

Answer 1

Not entirely sure why you would like to corrupt a valid json, but this what you can do
$ var="yeah\nis\ntest\nmy\nscript"
$ echo "{
"mytable_test": [
{
"test1": "abc",
"test2": "def",
"test2": "ghi"
}hellotesting
],
"mytable": [
"test1",
"test2",
"test3"
]
}" | sed -E "s/hellotesting$/${var}/"
Output
{
mytable_test: [
{
test1: abc,
test2: def,
test2: ghi
}yeah
is
test
my
script
],
mytable: [
test1,
test2,
test3
]
}