grep json keys from output stream

Question

For instance I have a JSON file like this:

{
    "mac": "00:11:22:33:44:55",
    "name: "Test123",
    "ssid": "29321",
    "password": "txt",
    "data": {
        "test:": "no",
        "dev": "yes",
        "prod": false
    },
    "signals": [12, 34, 65, 93, 21],
}

I'd like to grep a particular JSON key (including subkeys) from data above, but when I cat that file or read a JSON file from somewhere else in the output stream, ie wget or curl.

So far I have tried only this:

cat json.txt | grep -o -E '([[:xdigit:]]{1,2}:){5}[[:xdigit:]]{1,2}'

This returns the "mac" key value, grep's it by a pattern, strips all the quotes in the output and it really works flawlessly!

I honestly haven't tried anything regardings JSON keys, since any regular-expression system is not my stronger point and I hope you'll all help me about this.

NOTE: I'm very limited on the system where I'll be running this, so the -P option is not available.

EDIT: Actually, we do have root access to devices. They're running on MIPS platform and we have no compilers on the system installed. All the apps we can install must be already precompiled, so I doubt I'll find jq or jshon for these devices.

If there's another tool, that'd be helpful, probably.

EDIT 2: Issuing command: akw --version, we get this response:

BusyBox v1.19.‎4 (2017-03-27 19:07:06 EEST) multi-call binary.

I would, but I'm very limited on my system where I'd be running this - can't install software, I have a limited version of grep, etc. — Zlatan Omerovic
– Zlatan Omerovic, Commented Apr 18, 2017 at 20:31
It's a system which comes on Wi-Fi broadband equipment from this vendor: ubnt.com - it's based on Linux, runs an old version of PHP 4 (or something), we don't have the root access to it; just a tmp directory where we can store our files, and/or execute available commands. — Zlatan Omerovic
– Zlatan Omerovic, Commented Apr 18, 2017 at 20:32
You don't need a compiler on the system to compile software for it. People professionally building software for these systems don't run compilers on little embedded devices either. Look up cross compilation. — Charles Duffy
– Charles Duffy, Commented Apr 18, 2017 at 21:36
Personally, I'm a big fan of Buildroot as tooling for building system images for arbitrary targets -- though it doesn't need to be a full system image; you could just as easily build a single static executable that way. — Charles Duffy
– Charles Duffy, Commented Apr 18, 2017 at 21:37

J. Doe · Accepted Answer · 2017-04-18 21:45:45Z

1

Well using jq would be the ideal option but you could use sed to close

sed -n '/ *"keyname": */{ s///; s/ *, *$//; s/"//g; p; }'

answered Apr 18, 2017 at 21:45

J. Doe

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1 Comment

mklement0 Over a year ago

With very specific constraints (line-based layout, retrieving scalars only, no awareness of hierarchy, …) this may work, but I suggest stating these constraints in your answer. Perhaps also show how to specify the key name as a variable.

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