json – Get Key and Value from JSON in Array with Check

Your original version isn't going to be evalable because the author name has spaces in it - it would be interpreted as running a command Doe with the environment variable AUTHOR set to John. There's also virtually never a need to pipe jq to itself - the internal piping & dataflow can connect different filters together.

You can make a much simpler version of the jq program:

jq -r '.SITE_DATA | to_entries | .[] | .key + "=\"" + .value + "\""'

which outputs:

URL="example.com"
AUTHOR="John Doe"
CREATED="10/22/2017"

There's no need for a map: .[] deals with taking each object in the array through the rest of the pipeline as a separate item, so everything after the last | is applied to each one separately. At the end, we just assemble a valid shell assignment string with ordinary + concatenation, including quotes around the value.

All the pipes matter here - without them you get fairly unhelpful error messages, where parts of the program are evaluated in subtly different contexts.

This string is evalable as long as the characters `, $, newline and null don't appear in the data:

eval "$(jq -r '.SITE_DATA | to_entries | .[] | .key + "=\"" + .value + "\""' < data.json)"
echo "$AUTHOR"

As ever when using eval, be careful that you trust the data you're getting, since if it's malicious or just in an unexpected format things could go very wrong.

An empty string is still a string, so .abc_severity? would give you an empty string, not null (or false). Also, note that the question mark means approximately "replace with null if this key does not exist". In the example, all three keys exist, and their values are not null.

If you had been using null for empty values, your jq expression would have looked like

.Severity = (.abc_severity // .def_severity // .ghi_severity )

The above expression would have picked the first of the three values that weren't null, testing the left-most first and going right, or null if all of them were null. But that won't work now as we have to deal with empty strings as if they were null.

We can do that by introducing a helper function (to reduce our typing a bit):

def n: if . == "" then null else . end;
.Severity = ((.abc_severity|n) // (.def_severity|n) // (.ghi_severity|n) // "")

Our helper function n returns the string as-is if it is not empty; otherwise, it returns null. With chained // operators, we pick the first value of the three that is not null, when seen through n, or the empty string if all three values are null.

Testing the above on the command line with your data:

$ jq 'def n: if . == "" then null else . end; .Severity = ((.abc_severity|n) // (.def_severity|n) // (.ghi_severity|n) // "")' file
{
  "name": "0230",
  "publish_date": "2007-08-18",
  "abc_severity": "",
  "def_severity": "medium",
  "ghi_severity": "negligible",
  "Severity": "medium"
}