Getting JSON value from cURL in Linux Bash [duplicate]

Question

I want to GET some json data from a server. I do this using:

UPDATE=$(curl -i -H "Accept: application/json" -H "Content-Type: application/json" --cookie "${COOKIE_NAME}" "${1}/update/${DEVICE_NAME}");

Before this, the server is authenticated. The ${1} is the server domain, ${DEVICE_NAME} is the name of the device requesting the update.

This returns a JSON as follows:

[{"_id":"54ff35887d8ef574029b9166","user":"54fe4313883bcec2c0ac0d64","__v":0,"created":"2015-03-10T18:18:48.023Z","status":"available","pbo_udid":"lemaker","installation_script":"","description":"Prints hello world to console","package_name":"helloworld_1.0-1.deb","name":"Hello World V1"}]

I want to now do 2 things:

Make sure data is returned (if no update is available, the server returns []
Extract data, for instance package_name

How do I do these in Linux bash script?

You will likely need to pass the JSON value to a CLI for a script processor that can deserialize the JSON string and extract the data you are looking for. (i.e. something like PERL, PHP, etc.). Of course, at that point, I would probably just write the entire logic to retrieve and extract the data in that scripting language. Outside of that, you are likely looking at putting together some awkward combination of sed, awk, etc. to, in essence, build a deserializer. — Mike Brant
– Mike Brant, Commented Mar 10, 2015 at 18:55
There are some really great tools for parsing JSON from bash; jq is one of them. — Charles Duffy
– Charles Duffy, Commented Mar 10, 2015 at 20:33

Charles Duffy · Accepted Answer · 2015-03-10 20:34:20Z

11

Much more easily and reliably done using jq or jsawk:

content=$(curl ...)
package_name=$(jq -r '.package_name' <<<"$content")

answered Mar 10, 2015 at 20:34

Charles Duffy

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1 Comment

Arun Jose Over a year ago

saved my day!! exactly what I was looking for! :D

score 4 · Accepted Answer · 2015-03-10 20:30:56Z

4

Assuming there's no nested array:

cat <<EOF | json_reformat | \
    sed -rne '/:/s@^\s+"(\w+)":\s+"([^"]+)",?@json_\1="\2"@gp'
[{"_id":"54ff35887d8ef574029b9166","user":"54fe4313883bcec2c0ac0d64","__v":0,"created":"2015-03-10T18:18:48.023Z","status":"available","pbo_udid":"lemaker","installation_script":"","description":"Prints hello world to console","package_name":"helloworld_1.0-1.deb","name":"Hello World V1"}]
EOF

returns

json__id="54ff35887d8ef574029b9166"
json_user="54fe4313883bcec2c0ac0d64"
json_created="2015-03-10T18:18:48.023Z"
json_status="available"
json_pbo_udid="lemaker"
json_description="Prints hello world to console"
json_package_name="helloworld_1.0-1.deb"
json_name="Hello World V1"

You need json_reformat for this to work.

EDIT : without json_reformat:

cat <<EOF | \
    sed -re 's@(\[|\]|\{|\})@@g' -e 's/,/\n/g' | \
    sed -re 's@"(\w+)":\s*"?([^"]*)"?@json_\1="\2"@g'
[{"_id":"54ff35887d8ef574029b9166","user":"54fe4313883bcec2c0ac0d64","__v":0,"created":"2015-03-10T18:18:48.023Z","status":"available","pbo_udid":"lemaker","installation_script":"","description":"Prints hello world to console","package_name":"helloworld_1.0-1.deb","name":"Hello World V1"}]
EOF

It returns (note the version number that is reformatted anyway):

json__id="54ff35887d8ef574029b9166"
json_user="54fe4313883bcec2c0ac0d64"
json___v="0"
json_created="2015-03-10T18:18:48.023Z"
json_status="available"
json_pbo_udid="lemaker"
json_installation_script=""
json_description="Prints hello world to console"
json_package_name="helloworld_1.0-1.deb"
json_name="Hello World V1"

You can now try parsing this text using eval or source it from stdin.

edited Mar 10, 2015 at 20:30

answered Mar 10, 2015 at 19:18

user4113344

6 Comments

Kousha Over a year ago

Thanks. Any way to use it without downloading json_format?? I don't want to install other files

user4113344 Over a year ago

It might be possible to enhance the sed script. What I like in json_reformat is it spares you the burden of verifying and sanitizing the received data.

user4113344 Over a year ago

See my edited response, without json_reformat.

Charles Duffy Over a year ago

Pipe content retrieved from a web page into eval? Are you trying to get your system rooted?

user4113344 Over a year ago

@charles-duffy Not mine, no... More seriously, this is a hint of course. Using the evil eval is certainly not the only option. There are few of them however as the OP wishes no supplemental package.

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