Github api not parsing multi line shell variables - json

Question

I've got a text param (from jenkins job dsl plugin) in jenkins configuration which allows you to enter a multi line comment. I'm using that variable for the body value when posting a release to a github repository from a shell script. I'm getting this error that says problem parsing json and I can't find a workaround. I'll try to give you an example below. Please help.
PERSONAL_ACCESS_TOKEN="random"
TAG_NAME="12.0.0"
VERSION_BUMP="major"
MIGRATION_DOCUMENT="This is first line
This is second line"
curl -i \
-H "Authorization: token ${PERSONAL_ACCESS_TOKEN}" \
-d '{"tag_name": "'"${TAG_NAME}"'", "name": "'"${VERSION_BUMP}"'", \
"body": "'"${MIGRATION_DOCUMENT}"'"}' \
https://github.deere.com/api/v3/repos/randomOrg/testRepo/releases

Answer 1

This
{ "a": "b
c" }
is invalid JSON because a string must not contain control characters such as newlines.
If you have a string containing newlines, you can convert them to \n using shell parameter expansion:
$ var='a
b'
$ echo "$var"
a
b
$ echo "${var//$'\n'/'\n'}"
a\nb
So, to feed your string into your JSON object, use
"body": "'"${MIGRATION_DOCUMENT//$'\n'/'\n'}"'"
at the end of your JSON object.
Also, if you use line continuation in single quotes such as
var='abc \
def'
then the backslash and the linebreak are literal:
$ echo "$var"
abc \
def
Don't use line continuation like that in single quoted strings.
All in all:
curl -i \
-H "Authorization: token ${PERSONAL_ACCESS_TOKEN}" \
-d '{"tag_name": "'"${TAG_NAME}"'", "name": "'"${VERSION_BUMP}"'", "body": "'"${MIGRATION_DOCUMENT//$'\n'/'\n'}"'"}' \
https://github.deere.com/api/v3/repos/randomOrg/testRepo/releases
If you really want to, you can still use line continuation, but it has to be in a double quoted context:
curl -i \
-H "Authorization: token ${PERSONAL_ACCESS_TOKEN}" \
-d '{"tag_name": "'"${TAG_NAME}"'", "name": "'"${VERSION_BUMP}"'", '"\
"'"body": "'"${MIGRATION_DOCUMENT//$'\n'/'\n'}"'"}' \
https://github.deere.com/api/v3/repos/randomOrg/testRepo/releases
As a side note, you shouldn't use all uppercase names for variables; those are reserved for environment variables, see the POSIX spec (fourth paragraph).