New parser: update-alternatives --query

The Debian alternatives system has a update-alternatives command which has a --query option which will:

Display information about the link group like --display does, but in a machine parseable way (since version 1.15.0, see section QUERY FORMAT below).

For example for the editor (omitting the Slaves output):

update-alternatives --query editor
Name: editor
Link: /usr/bin/editor
Status: manual
Best: /bin/nano
Value: /usr/bin/vim.basic

Alternative: /bin/nano
Priority: 40

Alternative: /usr/bin/nvim
Priority: 30

Alternative: /usr/bin/vim.basic
Priority: 30

Alternative: /usr/bin/vim.tiny
Priority: 15

Perhaps this might be a useful new parser for jc, the Ansible alternatives module is only able to set alternatives, not read them, so I’ve written some Bash to use as a Ansible facts.d script for converting the output into JSON:

#!/usr/bin/env bash

set -euo pipefail

jo $(
  echo "${1}"=$( 
    if query=$(update-alternatives --query "${1}")
    then
      declare -a alternatives=()
      readarray -t alternatives < <(grep -e '^Alternative' <<< "${query}" | sed 's/Alternative: //')
      declare -a priorities=()
      readarray -t priorities < <(grep -e '^Priority' <<< "${query}" | sed 's/Priority: //')
      jo name="${1}" link=$(
        grep ^Link <<< "${query}" | sed 's/^Link: //'
      ) value=$(
        grep ^Value <<< "${query}" | sed 's/^Value: //'
      ) best=$(
        grep ^Best <<< "${query}" | sed 's/Best: //'
      ) alternatives=$(
        jo -a $(
          i=0
          while [[ "${i}" -lt "${#alternatives[@]}" ]]
          do
            jo path="${alternatives[${i}]}" priority="${priorities[${i}]}" 
            ((i++))
          done
        )
      )
    else
      jo state=absent
    fi
  )
)

Running this script with an argument, for example editor results in:

{
  "editor": {
    "name": "editor",
    "link": "/usr/bin/editor",
    "value": "/usr/bin/vim.basic",
    "best": "/bin/nano",
    "alternatives": [
      {
        "path": "/bin/nano",
        "priority": 40
      },
      {
        "path": "/usr/bin/nvim",
        "priority": 30
      },
      {
        "path": "/usr/bin/vim.basic",
        "priority": 30
      },
      {
        "path": "/usr/bin/vim.tiny",
        "priority": 15
      }
    ]
  }
}

[chriscroome]

The Ansible role I was planning to use to test the jc JSON update-alternatives --query output doesn’t seem to work for alternatives with lots of slaves like aptitude and editor and I won’t have time to look at this more until next week sometime – however I can’t see any jc bugs 😃

[kellyjonbrazil]

Nice! Let me know if you run into any other issues. I’m packaging v1.18.8 now. It’s already on PIP and the binaries should be in github Releases soon.

It would be possible to output YAML in addition to JSON. I might think about that for v1.19.0. Maybe open a feature request issue so we can track it.