Parse json from curl using shell

Question

When I curl to my URL, I get a JSON in the following format:

{"busyexecutors":0,
 "computers":[{"displayName":"Master","actions":[{},{},{}]},
              {"displayName":"137.0.01","actions":[{},{},{}]}]}

I want to extract only displayName where it's not equal to Master. So the output should be "137.0.0.1".

Let me know whether I can achieve this without external utilities like jq.

"I don't want to use extra utilities" - why? Portability? And how broad is your "like" - is Ruby okay (as it's installed on most current Unix-likes)? Because doing this in pure shell is somewhat fragile. — Amadan
– Amadan, Commented Oct 21, 2015 at 1:09
I agree with Amadan. Either you are using jq, or you are using something like python and ruby. Pure shell is simply not capable of handling this. — ljk321
– ljk321, Commented Oct 21, 2015 at 1:28
Thanks Amadan & skyline..wanted to know whether its possible with just shell. i don't understand ..what do you mean by fragile. — ayniam
– ayniam, Commented Oct 21, 2015 at 5:35
Shell utilities are typically line-oriented, whereas structured file formats very often exhibit variability in whitespace, including line breaks; so creating a parser for a structured file format using line-oriented tools tends to produce code which has a number of corner cases where results are invalid and incorrect, or the program simply aborts. This is a FAQ; see e.g. blog.codinghorror.com/parsing-html-the-cthulhu-way (the topic is HTML and regex but it extends readily to JSON and cut | head | tac | rev). — tripleee
– tripleee, Commented Nov 10, 2015 at 7:44

chepner · Accepted Answer · 2015-10-21 02:55:08Z

2

There are few good reasons not to use a proper JSON parser when working with JSON.

jq -r '.computers | .[].displayName | select(.!="Master")' <<EOF
{"busyexecutors":0,
 "computers":[{"displayName":"Master","actions":[{},{},{}]},
          {"displayName":"137.0.01","actions":[{},{},{}]}]}
EOF

answered Oct 21, 2015 at 2:55

chepner

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Comments

Zombo · Accepted Answer · 2015-10-21 16:53:13Z

1

As has been noted, this is a bad idea. However, if you insist to do it:

#!/usr/bin/awk -f
{
  split($0, z, /"/)
  for (y in z)
    if (z[y] == "displayName")
      if (z[y+2] != "Master")
        print z[y+2]
}

edited Oct 21, 2015 at 16:53

answered Oct 21, 2015 at 1:37

Zombo

1

1 Comment

Amadan Over a year ago

Strictly speaking, awk is also a utility... :P

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