jq -r bash cmd

https://www.baeldung.com/linux/jq-command-json 

The command jq -r 'select(.Update) | .Path + "@" + .Update.Version' is used within a shell script to filter and format JSON output from the go list -u -m -json all command. Here’s a detailed breakdown of what each part of the command does:

Explanation of the Command

jq -r

• jq: A lightweight and flexible command-line JSON processor. It allows you to parse, filter, and manipulate JSON data.
• -r: This option stands for "raw output." It outputs the filtered and transformed results as plain text instead of JSON, which is often easier to use in shell scripts.

'select(.Update)'

• select(.Update): This is a filter expression that selects only those JSON objects where the .Update field exists and is not null.
  • select: A jq function that filters JSON objects based on a condition.
  • .Update: A field in the JSON object output by go list -u -m -json all. This field contains update information for each Go module if an update is available.

'| .Path + "@" + .Update.Version'

• |: A pipe operator that passes the filtered results from the left side (select(.Update)) to the right side.
• .Path: This represents the Path field in the JSON object, which contains the module path (e.g., github.com/pkg/errors).
• + "@": This concatenates the module path with the "@" symbol, used to specify a version in Go modules.
• .Update.Version: This accesses the Version field within the Update object, which specifies the new version available for the module.

Combined Effect

The command as a whole does the following:

1. Filter Modules with Updates: select(.Update) filters out all the modules that do not have an available update. Only the modules with the .Update field present are passed to the next step.
2. Format Output: For each filtered module, the output is formatted as <module-path>@<new-version>. For example, if the module github.com/pkg/errors has an update to version v0.9.2, it outputs github.com/pkg/errors@v0.9.2.

Example

Assume you have a JSON output from go list -u -m -json all like this:

json
[
  {
    "Path": "github.com/pkg/errors",
    "Version": "v0.9.1",
    "Update": {
      "Version": "v0.9.2"
    }
  },
  {
    "Path": "golang.org/x/sys",
    "Version": "v0.0.0-20220315054443-0e35b0f21f97",
    "Update": {
      "Version": "v0.0.0-20220315190503-a33c662eeddc"
    }
  }
]

Running the jq command would filter and format it like this:

sh
github.com/pkg/errors@v0.9.2
golang.org/x/sys@v0.0.0-20220315190503-a33c662eeddc

This output is plain text and can be easily used in subsequent commands, such as go get, to update each module.

Usage in Shell Scripts

In a shell script, this output can be looped over to update all the dependencies that have updates available:

sh
modules=$(go list -u -m -json all | jq -r 'select(.Update) | .Path + "@" + .Update.Version')

for module in $modules; do
    echo "Updating $module"
    go get $module
done

go mod tidy

• modules=$(...): Executes the command within $(...) and stores the result in the modules variable.
• for module in $modules; do ... done: Iterates over each module and runs go get to update it.

This approach ensures that only the modules with available updates are processed and updated efficiently.