conky using a function call within an if statement

Question

How do I call a function after loading it in conkyrc? For example:

I'm trying to get the active interface name which is returning properly

${lua conky_findInterface} #gives me device name

function conky_findInterface()
  local handle = io.popen('ip a | grep "state UP" | cut -d: -f2 | tr -d " "')
  local result = handle:read('*a'):gsub('\n$','')
  handle:close()
  return result
end

How do I use it more dynamically? Such as :

${if_up ${lua_parse "${lua conky_findInterface}"}} #this does not work nor do my other variations
Hello
${else}
Goodbye
${endif}

Answer 1

It seems that a conky if statement argument can't be a string, so a string returned by a Lua function won't work. For example, where my interface is "enp2s0", the statement ${if_up enp2s0} will work, but ${if_up "enp2s0"} will not.

A workaround is to include the entire conky if statement in a Lua function. For example:

function findInterface()
  local handle = io.popen('ip a | grep "state UP" | cut -d: -f2 | tr -d " "')
  local result = handle:read('*a'):gsub('\n$','')
  handle:close()
  return result
end

function conky_ifupInterface()
  local ifup = "${if_up " .. findInterface() .. "}"
  ifup = ifup .. "Hello${else}"
  ifup = ifup .. "Goodbye${endif}"
  return ifup
end

The function conky_ifupInterface() is then called in conkyrc with the line:

${lua_parse conky_ifupInterface}

Unfortunately, just returning the first line of the if statement isn't sufficient to satisfy the lua_parse operator. The entire statement through the ${endif} has to be returned.

Note that the current implementation of findInterface will cause the conky config to crash on a call to conky_ifupInterface if the interface is down because findInterface will return a null value, resulting in the if statement beginning with ${if_up }. To make it work for testing, I did the following quick and dirty bit...

function findInterface()
  local handle = io.popen('ip a | grep "state UP" | cut -d: -f2 | tr -d " "')
  local result = handle:read('*a'):gsub('\n$','')
  handle:close()
  if result == "" then
    handle = io.popen('ip a | grep "state DOWN" | cut -d: -f2 | tr -d " "')
    result = handle:read('*a'):gsub('\n$','')
    handle:close()
  end
  return result
end

Yuck! I'm sure you can do better. :^)