At the end of the 8th line, I want to append content of another text file using sed.

When running the command

```
sed -i "8s/$/$(sed 's:/:\\/:g' recentchanges.txt)/" message2.json  

```

I get the error

```none
sed: -e expression #1, char 56: unknown option to `s'

```

Whereas `sed 's:/:\\/:g' recentchanges.txt` works and I get the content of the text file as expected.

What's wrong in my sed command? Let me know if there are any alternate ways to update the same file like awk etc.

Content of message2.json
========================

```
{
   "Subject": {
       "Data": "Test email sent using the AWS CLI",
       "Charset": "UTF-8"
   },
   "Body": {
       "Text": {
           "Data": "This is the message body in text format.",
           "Charset": "UTF-8"
       },
       "Html": {
           "Data": "This message body contains HTML formatting. It can, for example, contain links like this one: <a class=\"ulink\" href=\"http://docs.aws.amazon.com/ses/latest/DeveloperGuide\" target=\"_blank\">Amazon SES Developer Guide</a>.",
           "Charset": "UTF-8"
       }
   }
}

```

======================================

Content of recentchanges.txt
============================

```
Mon, 13 Apr 2020 11:49:26 +0530   User1 // Job1
Mon, 13 Apr 2020 11:18:26 +0530   User2 // Job2
Mon, 13 Apr 2020 13:03:59 +0530   User3 // Job3

```

================================================

Expected output
---------------

```
{
   "Subject": {
       "Data": "Test email sent using the AWS CLI",
       "Charset": "UTF-8"
   },
   "Body": {
       "Text": {
        "Data": 
        " Mon, 13 Apr 2020 11:49:26 +0530   User1 = Job1 \n  Mon, 13 Apr 2020 11:18:26 +0530 User2 = Job2 \n Mon, 13 Apr 2020 13:03:59 +053   User3 = Job3 ",
        "Charset": "UTF-8"
       },
       "Html": {
           "Data": "This message body contains HTML formatting. It can, for example, contain links like this one: <a class=\"ulink\" href=\"http://docs.aws.amazon.com/ses/latest/DeveloperGuide\" target=\"_blank\">Amazon SES Developer Guide</a>.",
           "Charset": "UTF-8"
       }
   }
}

```