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Update(start): answer the following line and you have answered the full question:

Why does the following:

echo '{"ipv4":["192.168.64.193"]}'|jq .ipv4[0]

Give this error:

no matches found: .ipv4[0]

Update(end)

I m trying to create a list variable, containing the values from "ipv4" from this json:

{
    "list": [
        {
            "ipv4": [
                "192.168.64.193"
            ],
            "name": "node2",
            "release": "20.04 LTS",
            "state": "Running"
        },
        {
            "ipv4": [
                "192.168.64.192"
            ],
            "name": "node1",
            "release": "20.04 LTS",
            "state": "Running"
        }
    ]
}

HOSTS is a list of the ip addresses:

UPDATE: Thanks to @Kusalananda I am using this in the script HOSTS+=$(echo $i|jq '.ipv4[0]')

get_hosts(){
  unset HOSTS
  # unset NAMES
  jq -c '.list[]' file.json | while read i; do
      HOSTS+=$(echo $i | jq .ipv4)
      # NAMES+=$(echo $i | jq .name)
  done
  echo $HOSTS
  # echo $HOSTS
}

I get:

[
  "192.168.64.193"
][
  "192.168.64.192"
]

But I need:

  "192.168.64.193"
  "192.168.64.192"

So I tried:

...
HOSTS+=$(echo $i | jq .ipv4[0])
...

But then I get:

get_hosts:3: no matches found: .ipv4[0]
get_hosts:3: no matches found: .ipv4[0]

Note: this is one of the lines in the loop:

{"ipv4":["192.168.64.193"],"name":"node2","release":"20.04 LTS","state":"Running"}
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1 Answer 1

Reset to default
3

The unquoted string .ipv4[] is a shell globbing pattern. This pattern does not match any existing files and the shell you are using is configured to generate an error (like zsh does by default) rather than to retain the pattern unexpanded (like bash does by default).

Quote the expression used with jq:

echo '{"ipv4":["192.168.64.193"]}' | jq '.ipv4[0]'

To extract all IP addresses from the data that you provide in the question, get all elements of all ipv4 arrays of the list array:

$ jq -r '.list[].ipv4[]' file
192.168.64.193
192.168.64.192

It's unlikely that you need to put these values into an array. Instead, read them one by one and do whatever you need to do to them:

jq -r '.list[].ipv4[]' file |
while IFS= read -r ipaddr; do
    # use "$ipaddr" here
done

To read the names and the first IP address for each name:

jq -r '.list[] | [ .name, .ipv4[0] ] | @tsv' file |
while IFS=$'\t' read -r name ipaddr; do
    # use "$name" and "$ipaddr" here
done

The @tsv operator produces tab-delimited output of an array, and we use it here to pair up the name with the corresponding IP address for each entry in the list array.

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6
  • Thanks, very good answer - the thing is that I actually need both "ipv4" and"name" to two arrays :-| Commented Jul 27, 2022 at 9:50
  • I ended up doing: HOSTS+=$(echo $i | jq '.ipv4[0]') and same for NAMES. Thanks again! Commented Jul 27, 2022 at 9:55
  • 1
    @ChrisG. You really don't need to do that. See update. Commented Jul 27, 2022 at 10:05
  • Ok, interesting "@tsv" and IFS. Not aware of these, thanks - much better Commented Jul 27, 2022 at 10:12
  • 1
    @ChrisG. IFS is the character that the shell will split the input on when reading with read. The last loop in my answer uses this to split the input on tabs, into the two variables name and ipaddr. Run the jq command by itself to see what the loop gets as input. Commented Jul 27, 2022 at 10:14

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