Draw vertical line at the first bar of the month in tradingview's pine script

Question

I'd like to draw a vertical dashed line at every first bar of a month (for daily and weekly charts) or a year (for monthly charts). How can I do that? I don't know how to get those bar indexes.

Addition: I read in this post that "line.new" has a restriction to 54 lines max per indicator. But when using the plot function in histogram style (=plot only single vertical histogram bars), I cannot plot dashed lines... and I prefer a solution with dashed lines...

Answer 1

This is an adaptation of midtownsk8rguy's code here:

//@version=4
study("Periodic Vline", overlay=true)
p = timeframe.ismonthly ? "12M" : "M"
vline(BarIndex, Color, LineStyle, LineWidth) =>
    return = line.new(BarIndex, low - tr, BarIndex, high + tr, xloc.bar_index, extend.both, Color, LineStyle, LineWidth)
if change(time(p))
    vline(bar_index, #FF800080, line.style_dashed, 1)