jq

jq is a lightweight and flexible command-line JSON processor.

Slackbuild

   1 cd /tmp
   2 wget https://slackbuilds.org/slackbuilds/14.2/system/jq.tar.gz
   3 tar xvzf jq.tar.gz
   4 cd jq
   5 wget https://github.com/stedolan/jq/releases/download/jq-1.4/jq-1.4.tar.gz
   6 ./jq.SlackBuild
   7 installpkg /tmp/jq-1.4-i486-1_SBo.tgz

jq-1.4-i486-1_SBo.tgz

Change values

test.json

   1 {
   2   "keyx":12,
   3   "keyz":"ddff"
   4 }

   1 jq '.keyx = 55 | .keyz = "otherVal"' test.json