Read JSON file & parse to get element values in shell script

Question

I have a json file names test.json with the below content.

{
        "run_list": ["recipe[cookbook-ics-op::setup_server]"],
    "props": {
        "install_home": "/test/inst1",
            "tmp_dir": "/test/inst1/tmp",
        "user": "tuser
                 }
}

I want to read this file into a variable in shell script & then extract the values of install_home,user & tmp_dir using expr. Can someone help, please?

props=cat test.json

works to get the json file into a variable. Now how can I extract the values using expr. Any help would be greatly appreciated.

Don't use `expr` or regular expressions (anticipating some nasty regex-based answers). Use a proper JSON parser such as `jq`. — Tom Fenech, Nov 05 '15 at 14:11
The sample JSON supplied is malformed, it's missing a closing double quote on the line that says `tuser`. — Stephen Quan, May 25 '18 at 04:03
Possible duplicate of https://stackoverflow.com/questions/1955505/parsing-json-with-unix-tools — Stephen Quan, Jul 12 '21 at 01:52

score 5 · Answer 1 · answered Sep 04 '19 at 06:57

Install jq

yum -y install epel-release
yum -y install jq

Get the values in the following way

install_home=$(cat test.json  | jq -r '.props.install_home')
tmp_dir=$(cat test.json  | jq -r '.props.tmp_dir')
user=$(cat test.json  | jq -r '.props.user')

score 3 · Answer 2 · answered Nov 05 '15 at 14:46

For a pure bash solution I suggest this:
github.com/dominictarr/JSON.sh
It could be used like this:

./json.sh -l -p < example.json

print output like:

["name"]        "JSON.sh"
["version"]     "0.2.1"
["description"] "JSON parser written in bash"
["homepage"]    "http://github.com/dominictarr/JSON.sh"
["repository","type"]   "git"
["repository","url"]    "https://github.com/dominictarr/JSON.sh.git"
["bin","JSON.sh"]       "./JSON.sh"
["author"]      "Dominic Tarr <dominic.tarr@gmail.com> (http://bit.ly/dominictarr)"
["scripts","test"]      "./all-tests.sh"

From here is pretty trivial achive what you are looking for

score 3 · Answer 3 · answered Mar 15 '21 at 10:52

jq is a dedicated parser for JSON files. Install jq.

values in the json can be retrieved as:

jq .<top-level-attr>.<next-level-attr> <json-file-path>

if JSON contains an array

jq .<top-level-attr>.<next-level-array>[].<elem-in-array> <json-file-path>

if you want a value in a shell variable

id = $(jq -r .<top-level-attr>.<next-level-array>[].<next-level-attr> <json-file-path>)

echo id

use -r if you need unquoted value

Stephen Quan · Answer 4 · 2021-07-12T01:42:23.493

For simple JSON, it may be treated as a plain text file. In that case, we can use simple text pattern matching to extract the information we need.

If you observe the following lines:

    "install_home": "/test/inst1",
        "tmp_dir": "/test/inst1/tmp",
    "user": "user"

There exists a pattern on each line that can be described as key and value:

"key" : "value"

We can use perl with regular expressions to exact the value for any given key:

"key" hardcoded for each case "install_home", "tmp_dir" and "user"
"value" as (.*) regular expression

Then we use the $1 matching group to retrieve the value.

i=$(perl -ne 'if (/"install_home": "(.*)"/) { print $1 . "\n" }' test.json)
t=$(perl -ne 'if (/"tmp_dir": "(.*)"/) { print $1 . "\n" }' test.json)
u=$(perl -ne 'if (/"user": "(.*)"/) { print $1 . "\n" }' test.json)

cat <<EOF
install_home: $i
tmp_dir     : $t
user        : $u
EOF

Which outputs:

install_home: /test/inst1
tmp_dir     : /test/inst1/tmp
user        : tuser

While this might work for a simple json, for more complex json using regex will be a nightmare! — njminchin, Jul 09 '21 at 11:27

Read JSON file & parse to get element values in shell script

4 Answers4