A tiny CLI weather {Rapp}ort

tl;dr

The {weva} R package contains a titchy command-line interface (CLI) to present an opinionated micro-weather report.

Building some {Rapp}ort

I’m spending more time in the terminal.

So I’ve been making little CLI concepts:

• jot for recording notes
• pet for a persistent cyberpet
• tyle for a roguelike-like

These are all written in Python, which seems a more natural choice for this purpose than R¹.

But I was pleased to see a recent blog post about a new release of {Rapp}, an R package to help create CLIs.

So obviously I needed to try it out.

CLImate

But a CLI for what?

My colleagues and I have enjoyed twee weather CLIs of late, like weathr and wttr.in.

So, because I have no imagination: introducing the concept {weva} (‘wevvah’²) R package.

It does way less than those other examples and doesn’t have fun ASCII graphics. It’s just a simple toy project to see how {Rapp} works, with no guarantees. Is that enough disclaimers?

Along with {Rapp}, this was made possible by the:

• free APIs Open-Meteo and postcodes.io³, which do not require a login
• the tidyverse packages {httr2} and {lubridate}

R console

From the R console, you could install⁴ {weva} from GitHub like:

pak::pak("matt-dray/weva")

You then use a {weva} function to install the CLI tool:

weva::install_cli()

This will print the install location of the CLI, if successful.

Terminal

From a terminal—not the R console—you can use weva to look up weather for a given UK postcode⁵.

Let’s compare Lands End (‘top’ of mainland Britain) to John o’ Groats (‘bottom’)⁶ as I write this.

weva tr197aa

now 10.9°C ☁️ | +1h 11.3°C ☁️ 

weva kw14yr

now 6.1°C ☁️ | +1h 6.3°C 🌧️🪶 

The one-line display has segments for the current and future temperature and weather. There are emoji modifiers for heavy, light and freezing versions of some weather types.

Surprise, it’s early March everywhere in Britain.

Hopefully your day will be brightened by the styling with ANSI escape codes, assuming your terminal supports them.

Options

You can add some flags to adjust the settings. Use --hour (or its shortcut -h) to adjust the number of hours for the forward-look. Let’s look one day ahead.

weva tr197aa -h 24

now 10.9°C ☁️ | +24h 7.7°C 🌧️🪶 

So there’s light drizzle this time tomorrow and it will be cooler (did I mention it’s early March in Britain).

Note that you can only look at forecasts up to the end of the day after tomorrow⁷.

Use the --extremes (-e) flag to also print a segment with today’s low and high temperatures. You can compound these options:

weva tr197aa -h 24 -e

now 10.9°C ☁️ | +24h 7.7°C 🌧️🪶 | today 9.3°C to 12°C 

Well, ‘extremes’ is perhaps a bit extreme for this temperature range.

Time is hard

‘Now’ and ‘later’ in this context are actually a bit awkward.

The Open-Meteo API returns the ‘current’ time as a quarter-hour increment, while ‘hourly’ information is the top of the hour.

My low-effort solution was to round ‘now’ to the nearest hour and declare ‘+1 hour’ as the hour after that.

In addition, the hourly data is returned for the whole of the current day (i.e. some of it is from the past). That means we have to match the rounded ‘now’ time to the list of times for today to get its index, then add the user-supplied --hours to find the details for the correct time in the future.

So you can only ask for a forecast for the rest of today or the following two full days.

That’s a bit confusing, so you can use the --datetime (-d) option to expose the datetimes for the data in each segment of the report.

weva tr197aa -h 24 -e -d

2026-03-01 10:00 10.9°C 🌧️🪶 | 2026-03-02 10:00 7.7°C 🌧️🪶 | 2026-03-01 9.3°C to 12°C 

As I write, it’s 10:06 on 1 March 2026. That’s rounded to 10:00 for the ‘now’ time. And so 24 hours from now is 10:00 tomorrow: 2 March 2026.

Inside the crystal ball

What’s actually happening in the code?

{weva} is just a normal R package with some exported functions to get_latlon(), get_weather() and write_report().

But there’s one difference: a script under exec/ that contains R code that {Rapp} will reinterpret (magically?) into a CLI.

At time of writing it looks like this:

#!/usr/bin/env Rapp
#| name: weva
#| description: A micro weather report with 'Open-Meteo' and 'postcodes.io' APIs

#| description: A UK postcode
postcode <- NULL

#| description: Hours from now for the 'later' segment (up to three days)
#| short: h
hours <- 1L

#| description: Show API and calculated datetimes in 'now' and 'later' segments?
#| short: d
datetimes <- FALSE

#| description: Show a segment for today's min and max temperatures?
#| short: e
extremes <- FALSE

get_latlon(postcode) |>
  get_weather() |>
  write_report(
    hours_to_forecast = hours,
    show_datetimes = datetimes,
    show_extremes = extremes
  ) |>
  cat()

Note in this file:

• the shebang (#!)⁸, which gives the path to where {Rapp} is installed
• the hashpipes (#|) for documenting the CLI and its options
• that everything else is normal R code

{Rapp} interprets postcode <- NULL as a required positional argument for weva. You can just type the postcode without a flag.

Conversely, the remaining options must be named, though short names can be used to save typing. --hours (-h) is interpreted as an integer with a default of 1 --datetimes and --extremes (-d, -e) are off (FALSE) by default, but the user can just use the flag without an argument to turn it on.

What’s also nice is that {Rapp} gives us --help (and --help-yaml) for free, based on our variable documentation.

weva --help

Usage: weva [OPTIONS] <POSTCODE>

A micro weather report with 'Open-Meteo' and 'postcodes.io' APIs

Options:
  -h, --hours <HOURS>             Hours from now for the 'later' segment (up to
                                  three days)
                                  [default: 1] [type: integer]
  -d, --datetimes / --no-datetimes  Show API and calculated datetimes in 'now'
                                  and 'later' segments?
                                  [default: false]
                                  Enable with `--datetimes`.
  -e, --extremes / --no-extremes  Show a segment for today's min and max
                                  temperatures?
                                  [default: false]
                                  Enable with `--extremes`.

Arguments:
  <POSTCODE>  A UK postcode

In short, {Rapp} lets you write ‘normal’ looking R code that gets interpreted into a CLI with various types of options.

That’s quite a neat, low-effort way to create a CLI.

{Rapp}ing up

{weva} is [repeated disclaimers]. It would be easy to get carried away and build something even more complex. I’ve achieved the content and learning I wanted, so I stop here.

In fact, I already used this tool yesterday before a trip⁹. I discovered the day was going to be overcast with some showers. Who could have guessed?

But on more variable days, I’m reminded of Fran’s observation when faced with differing forecasts:

I had better go outside and see who’s right

Very wise.

Environment

Session info

Last rendered: 2026-03-07 13:30:38 GMT

R version 4.5.2 (2025-10-31)
Platform: aarch64-apple-darwin20
Running under: macOS Sequoia 15.6.1

Matrix products: default
BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib 
LAPACK: /Library/Frameworks/R.framework/Versions/4.5-arm64/Resources/lib/libRlapack.dylib;  LAPACK version 3.12.1

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

time zone: Europe/London
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
 [1] htmlwidgets_1.6.4 compiler_4.5.2    fastmap_1.2.0     cli_3.6.5        
 [5] tools_4.5.2       htmltools_0.5.8.1 yaml_2.3.12       rmarkdown_2.29   
 [9] knitr_1.50        jsonlite_2.0.0    xfun_0.52         digest_0.6.37    
[13] rlang_1.1.7       evaluate_1.0.4   

Footnotes

1. I don’t want to simply run scripts from the command line, which is what Rscript is for.

2. With a respectful cockney accent.

3. Packages {openmeteo} and {PostcodesioR} wrap their respective APIs, but I minimised the dependencies by querying myself with {httr2}.

4. Remember: you shouldn’t trust ‘some dude’ telling you to install random stuff from the internet.

5. For my purposes I don’t care about weather anywhere except in the UK. I’m more likely to know the postcode than latitude-longitude, so I’m happy to limit the tool in this way.

6. Actually these postcodes are for the First & Last House pub and the John o’ Groats brewery.

7. We don’t need to forecast beyond that, because we know the weather’s going to be really dicey and unpredictable.

8. Important disambiguation.

9. Amusingly, given my time-related pains in {weva}, we went to Greenwich.