Update JSON based on condition using jq

Question

Supposing that I have a JSON file that looks like this:

{
  "name": "tom",
  "scripts": {
    "webpack": "webpack --progress --colors --watch"
  },
  "dependencies": {
  },
  "devDependencies": {
    "webpack": "^2.2.1"
  }
}

I would like to be able to specify a package by name, find the corresponding entry in either dependencies or devDependencies and update the value.

The closest I got was this:

$ jq --arg p webpack --arg v 1.2.3 'to_entries | map(
   if (.value[$p]? | startswith("^")?) then 
      .value[$p] = $v
   else . 
   end
) | from_entries' file.json

Which updates the value but also removes the dependencies and the name property:

{
  "scripts": {
    "webpack": "webpack --progress --colors --watch"
  },
  "devDependencies": {
    "webpack": "1.2.3"
  }
}

How can I update the desired value without affecting the other properties in the original JSON?

Jeff Mercado · Accepted Answer · 2017-02-21 18:16:26Z

1

Try this instead:

$ jq --arg p webpack --arg v 1.2.3 '
def update_package($package; $version):
    if has($package) then .[$package] = $version
    else . end;
.dependencies |= update_package($p; $v)
    | .devDependencies |= update_package($p; $v)' project.json

update_package/2 will only update the dependency object if it actually references the given project, otherwise it is left alone. Apply to both dependencies and devDependencies.

The problem with your original filter that was removing the dependencies object was that since the project didn't exist, there was no corresponding value to update. By applying startswith on the nonexistent value, it caused an error. That error in turn was just ignored and effectively skipped the corresponding item in the map, thus losing that property.

For a quick fix to ensure this doesn't happen, don't ignore the error, provide an alternate value to use when the property doesn't exist.

.value[$p]?      | startswith("^")? # bad
.value[$p] // "" | startswith("^")  # better

edited Feb 21, 2017 at 18:16

answered Feb 21, 2017 at 18:09

Jeff Mercado

136k34 gold badges268 silver badges282 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Tom Fenech Over a year ago

That's great, thanks. Is there a way to call the function in a loop? I was trying to adapt your code to use foreach [.dependencies, .devDependencies] but couldn't get it to work.

Jeff Mercado Over a year ago

You could do this: .["dependencies","devDependencies"] |= update_package($p; $v)

Jeff Mercado Over a year ago

or even (.dependencies,.devDependencies) |= update_package($p; $v)

Tom Fenech Over a year ago

I decided to "inline" the function in the end (.dependencies,.devDependencies) |= if has($p) then .[$p] = $v else . end.

peak · Accepted Answer · 2017-02-22 07:08:31Z

1

Using your approach, it would be better to use map_values:

map_values(if type == "object" 
           then with_entries( if .key == $p and (.value | startswith("^")?) 
                              then .value = $v else . end )
           else . end)

You might also like to consider using walk/1:

walk(if type == "object" and has($p) and (.[$p]|startswith("^"))
     then .[$p] = $v else . end)

The solution using walk/1 will examine the JSON entity recursively. If your jq does not have walk, its definition in jq can readily be found by googling.

Robust solution using when/2

def when(p;q): if p//false then q else . end;

map_values( when(type == "object";
                 with_entries( when( .key == $p and (.value | startswith("^")?);
                                     .value = $v) )) )

edited Feb 22, 2017 at 7:08

answered Feb 21, 2017 at 18:38

peak

119k21 gold badges185 silver badges218 bronze badges

4 Comments

Tom Fenech Over a year ago

Sorry, I'm afraid my example was over-simplified - there are other properties in the file which cause this approach to fail. I've edited my question to add a property with a string value.

peak Over a year ago

The answer using map_values has been modified in accordance with the modified question; the answer using walk does not need to be modified, though of course it can be made more robust.

Tom Fenech Over a year ago

I think I was over-complicating things by trying to traverse the object when really I knew that the change needed to be made in one of two places. Where does the convention of adding /N to the name of functions come from?

peak Over a year ago

The name/arity notation has been used for a long time in Prolog and Erlang, and more recently in Elixir and no doubt others.

Collectives™ on Stack Overflow

Update JSON based on condition using jq

2 Answers 2

4 Comments

Robust solution using when/2

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Robust solution using when/2

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related