Q:

jq + print properties from json file without removing the necessary backslash

we have the following json file:
more file.json

{
  "href" : "http://master02:8080/api/v1/clusters/HDP/configurations?type=kafka-env&tag=version1527250007610",
  "items" : [
    {
      "href" : "http://master02:8080/api/v1/clusters/HDP/configurations?type=kafka-env&tag=version1527250007610",
      "tag" : "version1527250007610",
      "type" : "kafka-env",
      "version" : 8,
      "Config" : {
        "cluster_name" : "HDP",
        "stack_id" : "HDP-2.6"
      },
      "properties" : {
        "content" : "\n#!/bin/bash\n\n# Set KAFKA specific environment variables here.\n\n# The java implementation to use.\nexport JAVA_HOME={{java64_home}}\nexport PATH=$PATH:$JAVA_HOME/bin\nexport PID_DIR={{kafka_pid_dir}}\nexport LOG_DIR={{kafka_log_dir}}\nexport KAFKA_KERBEROS_PARAMS={{kafka_kerberos_params}}\nexport JMX_PORT=9997\n# Add kafka sink to classpath and related depenencies\nif [ -e \"/usr/lib/ambari-metrics-kafka-sink/ambari-metrics-kafka-sink.jar\" ]; then\n  export CLASSPATH=$CLASSPATH:/usr/lib/ambari-metrics-kafka-sink/ambari-metrics-kafka-sink.jar\n  export CLASSPATH=$CLASSPATH:/usr/lib/ambari-metrics-kafka-sink/lib/*\nfi\n\nif [ -f /etc/kafka/conf/kafka-ranger-env.sh ]; then\n. /etc/kafka/conf/kafka-ranger-env.sh\nfi",
        "is_supported_kafka_ranger" : "true",
        "kafka_log_dir" : "/var/log/kafka",
        "kafka_pid_dir" : "/var/run/kafka",
        "kafka_user" : "kafka",
        "kafka_user_nofile_limit" : "128000",
        "kafka_user_nproc_limit" : "65536"
      }
    }
  ]

we build the following jq syntax in order to print the properties from the file.json
jq -r '.items[].properties | to_entries[]
       | "\"\(.key)\" : \"\(.value | gsub("\n";"\\n"))\","' file.json

"content" : "\n#!/bin/bash\n\n# Set KAFKA specific environment variables here.\n\n# The java implementation to use.\nexport JAVA_HOME={{java64_home}}\nexport PATH=$PATH:$JAVA_HOME/bin\nexport PID_DIR={{kafka_pid_dir}}\nexport LOG_DIR={{kafka_log_dir}}\nexport KAFKA_KERBEROS_PARAMS={{kafka_kerberos_params}}\nexport JMX_PORT=9997\n# Add kafka sink to classpath and related depenencies\nif [ -e "/usr/lib/ambari-metrics-kafka-sink/ambari-metrics-kafka-sink.jar" ]; then\n  export CLASSPATH=$CLASSPATH:/usr/lib/ambari-metrics-kafka-sink/ambari-metrics-kafka-sink.jar\n  export CLASSPATH=$CLASSPATH:/usr/lib/ambari-metrics-kafka-sink/lib/*\nfi\n\nif [ -f /etc/kafka/conf/kafka-ranger-env.sh ]; then\n. /etc/kafka/conf/kafka-ranger-env.sh\nfi",
"is_supported_kafka_ranger" : "true",
"kafka_log_dir" : "/var/log/kafka",
"kafka_pid_dir" : "/var/run/kafka",
"kafka_user" : "kafka",
"kafka_user_nofile_limit" : "128000",
"kafka_user_nproc_limit" : "65536",

but the problem is that output is without the backslash before double quota
example
instead to get in the output the following line 
 [ -e \"/usr/lib/ambari-metrics-kafka-sink/ambari-metrics-kafka-sink.jar\" ]

we get in the output: ( without the necessary backslash ) 
 [ -e "/usr/lib/ambari-metrics-kafka-sink/ambari-metrics-kafka-sink.jar" ]

please advice how to fix the jq syntax accordingly
.
.
.
example of expected results:
expected output
    "content" : "\n#!/bin/bash\n\n# Set KAFKA specific environment variables here.\n\n# The java implementation to use.\nexport JAVA_HOME={{java64_home}}\nexport PATH=$PATH:$JAVA_HOME/bin\nexport PID_DIR={{kafka_pid_dir}}\nexport LOG_DIR={{kafka_log_dir}}\nexport KAFKA_KERBEROS_PARAMS={{kafka_kerberos_params}}\nexport JMX_PORT=9997\n# Add kafka sink to classpath and related depenencies\nif [ -e \"/usr/lib/ambari-metrics-kafka-sink/ambari-metrics-kafka-sink.jar\" ]; then\n  export CLASSPATH=$CLASSPATH:/usr/lib/ambari-metrics-kafka-sink/ambari-metrics-kafka-sink.jar\n  export CLASSPATH=$CLASSPATH:/usr/lib/ambari-metrics-kafka-sink/lib/*\nfi\n\nif [ -f /etc/kafka/conf/kafka-ranger-env.sh ]; then\n. /etc/kafka/conf/kafka-ranger-env.sh\nfi",
    "is_supported_kafka_ranger" : "true",
    "kafka_log_dir" : "/var/log/kafka",
    "kafka_pid_dir" : "/var/run/kafka",
    "kafka_user" : "kafka",
    "kafka_user_nofile_limit" : "128000",
    "kafka_user_nproc_limit" : "65536"

A:

jq has several escaping modes you can use instead of your own quoting.
jq -r '.items[].properties | to_entries[] | (.key | @json) + ": " + (.value|@json) + ","' file.json

produces the output you want, I think. The @json formatter adds quotes and backslashes as necessary to preserve JSON-valid syntax, including double-quoting strings:
"content": "\n#!/bin/bash\n\n# Set KAFKA specific environment variables here.\n\n# The java implementation to use.\nexport JAVA_HOME={{java64_home}}\nexport PATH=$PATH:$JAVA_HOME/bin\nexport PID_DIR={{kafka_pid_dir}}\nexport LOG_DIR={{kafka_log_dir}}\nexport KAFKA_KERBEROS_PARAMS={{kafka_kerberos_params}}\nexport JMX_PORT=9997\n# Add kafka sink to classpath and related depenencies\nif [ -e \"/usr/lib/ambari-metrics-kafka-sink/ambari-metrics-kafka-sink.jar\" ]; then\n  export CLASSPATH=$CLASSPATH:/usr/lib/ambari-metrics-kafka-sink/ambari-metrics-kafka-sink.jar\n  export CLASSPATH=$CLASSPATH:/usr/lib/ambari-metrics-kafka-sink/lib/*\nfi\n\nif [ -f /etc/kafka/conf/kafka-ranger-env.sh ]; then\n. /etc/kafka/conf/kafka-ranger-env.sh\nfi",

The only bit of raw string manipulation required here is to add the ":"; otherwise it's just piping the key/value into the filter and it handles all the quoting. You could also use @json "\(.key): \(.value),", though I find that behaviour more trouble than it's worth.

If the excess comma on the last line is an issue, collect the values together and use join(str)instead:
jq -r '.items[].properties | [to_entries[] | @json "\(.key): \(.value)"] | join(",\n")' file.json

This puts all the strings into an array and then puts ,\n between each pair.

