jq select value from array

Question

I have the following JSON file with example values:

{
  "files": [{
    "fileName": "FOO",
    "md5": "blablabla"
  }, {
    "fileName": "BAR",
    "md5": "alaldlafj"
  }]
}

Now what I want is to return the md5 value where for example the fileName is "FOO". For this I have the following statement in jq:

cat <file>.json | jq '.[] | select(.fileName=="FOO")'

However response back is: jq: error (at <stdin>:11): Cannot index array with string "fileName"

What is the correct way to return the md5 value where the key fileName equals a certain argument?

Benjamin Loison · Accepted Answer · 2023-08-16 22:35:32Z

101

Found the answer:

cat <file>.json | jq -r '.files[] | select(.fileName=="FOO") | .md5'

edited Aug 16, 2023 at 22:35

Benjamin Loison

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answered Jun 1, 2016 at 11:11

Marvin Effing

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4 Comments

Brent D. Over a year ago

Why bring cat into this? You can simply jq -r '.files[] | select(.fileName=="FOO") | .md5' <file.json>

bitinerant Over a year ago

@BrentD. - You are right that your version is shorter and simpler. However, some such as myself strongly prefer the strictly left-to-right structure that beginning with cat provides, especially when pipes are involved.

Scott Centoni Over a year ago

A shorter, simpler line that maintains strict left-to-right ordering is <file.json jq -r '.files[] | select(.fileName=="FOO") | .md5'

karatedog Over a year ago

Thinking of newbies cat file.json is a bit more readable than <file.json. I'm also on the cat file.json side as mostly that file.json is a mock and when the script goes live, it will replaced by the real data source that might contain cleanup and filter commands all piped together and that jq is just the last part of a bigger equation.

jmunsch · Accepted Answer · 2021-09-30 23:56:04Z

13

to answer the more generic how to select value from array selecting all filenames:

cat results.json | jq '.files[] | .filename'

answered Sep 30, 2021 at 23:56

jmunsch

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1 Comment

Mika Riekkinen Over a year ago

The question was about selecting a specific field based on value of other field. Not about selecting all the fields.

Rob Paisley · Accepted Answer · 2020-08-04 10:24:35Z

7

or:

cat <file>.json | jq -r '.files[] | select(.fileName=="FOO").md5'

edited Aug 4, 2020 at 10:24

Rob Paisley

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answered Dec 3, 2019 at 17:33

Alex Berger

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1 Comment

Kevin Over a year ago

Welcome to Stackoverflow! Please consider reading this section to improve your answer. Can you provide an explanation for the code you have posted here?

Mz A · Accepted Answer · 2024-01-19 08:48:10Z

4

If you want to keep your item in the array, so do more of a filter you can do

cat <file>.json | jq -r '.files | map(select(.fileName=="FOO").md5)'

this would result in

['blablabla']

answered Jan 19, 2024 at 8:48

Mz A

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