jq error when looping through array: Cannot index array with string "<key>"

Question

I'm tryng to iterate over all element contain in the all index. Here is my json string :

{  
   "all":[  
      {  
            "id":"51a"
      },
      {  
            "id":"52b"
      },
      {  
            "id":"53c"
      }
    ]
}

I have tried to iterate with jq :

for id in $(jq '.all.id | keys | .[]' <<< "$json"); do
    echo "$id"
done

But I get this following error :

jq: error (at :9): Cannot index array with string "id"

I expect to get the following output :

51a
52b
53c

while IFS= read -r id; do ...; done < <(jq ...) is a better way to run that loop. Right now, if you have an id of *, a list of filenames in your current directory will be inserted (among other issues; consider that one a representative example). — Charles Duffy
– Charles Duffy, Commented May 20, 2019 at 13:37

Arkadiusz Drabczyk · Accepted Answer · 2019-05-20 13:59:50Z

2

Like that:

for id in $(jq -r '.all[].id' <<< "$json"); do
    echo "$id"
done

Notice that -r option has to be used if you want to remove double quotes:

 ·   --raw-output / -r:

       With this option, if the filter´s result is a string then
       it will be written directly to standard output rather than
       being formatted as a JSON string with quotes. This can be
       useful for making jq filters talk to non-JSON-based
       systems.

The entire script could look like that:

#!/usr/bin/env bash

json='{  
   "all":[  
      {  
            "id":"51a"
      },
      {  
            "id":"52b"
      },
      {  
            "id":"53c"
      }
    ]
}'

for id in $(jq -r '.all[].id' <<< "$json"); do
    echo "$id"
done

But as noted in the comments, for x in $(...) is an antipattern and should not be used: https://mywiki.wooledge.org/DontReadLinesWithFor.

To assign two indices to 2 separate variables:

#!/usr/bin/env bash

json='{
   "all":[
      {
            "id":"51a",
            "name":"Steve"
      },
      {
            "id":"52b",
            "name":"Phoebe"
      },
      {
            "id":"53c",
            "name":"Dino"
      }
    ]
}'

jq -r '.all[] | .id + " " + .name' <<< "$json" |
    while read -r id name; do
        echo id: "$id"
        echo name: "$name"
    done

edited May 20, 2019 at 13:59

answered May 20, 2019 at 12:28

Arkadiusz Drabczyk

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13 Comments

executable Over a year ago

Thank you for the answer ! I have found a workaround pastiebin.com/5ce29e47a50c5 but I'm going to use the code in the answer

executable Over a year ago

I'd like to know if it's possible to also extract an other element from the same array. Let's say I have id and name index with their value. How can I extract both ?

MSalters Over a year ago

@executable: jq is a fairly simple tool. It defines expressions to extract parts of the input, and a syntax to assemble the output. .all[].id is shorthand for .all | .[] | .id, and you want another member in addition to .id. So how should that second member be combined with .id ?

Arkadiusz Drabczyk Over a year ago

@executable: It could be something like this: for id in $(jq -r '.all[] | .id + " " + .name' <<< "$json"); do

executable Over a year ago

@Arkadiusz Drabczyk Thank you for the answer but is it possible to assign them separatly to variable ?

|

Dmitry · Accepted Answer · 2019-05-20 13:02:10Z

1

and here's an alternative solution based on a walk-path unix tool for JSON: jtc:

bash $ for id in $(jtc -qq -w'[all][:][id]' <<< "$json"); do  echo "$id"; done
51a
52b
53c
bash $

PS> Disclosure: I'm the creator of the jtc tool

answered May 20, 2019 at 13:02

Dmitry

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2 Comments

executable Over a year ago

What's different from jq ?

Dmitry Over a year ago

tools are drastically different. jq is a processor with own DSL with the scope of operations well beyond JSON data model. While jtc is a utility confined to the data model operations only. That difference let coming up with queries to manipulate source jsons a lot easier (but of course it's mho).

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