Sys.getenv() returns empty in Shiny Apps - r

Question

NOTE I edited the question, since the use of PG_HOST was causing confussion, but the spirit is the same
I am running a shiny app that needs read some environment variables.
That variables are defined before the shiny server starts. For example
export APPLE=apple
export PENCIL=pencil
In the global.R (or at the beggining of server.R is the same) I wrote the following code:
manzana <- Sys.getenv('APPLE')
lapiz <- Sys.getenv('PENCIL')
but those variables are empty.
If I run that code in the R console, both returns the correct value.
Whay this is not working? Whay is different the R console and the shiny app?
How I can get the real environment variables (in this fake example $APPLE and $PENCIL)?
Which is the correct way of configuring the shiny app?

Answer 1

First step is to understand reactivity. Check out the shiny tutorials.
using your example..kind of..heres an app the updates and sets variables that can be called numerous ways....
shiny_example <- function(){
server <- shinyServer(function(session,input,output){
the_slots <- list(Apple = 'apple',Green = 'green')
make_globs <- function(new_var = NULL){
if(!is.null(new_var)){
the_slots <<- append(the_slots,new_var)
}
}
glob_vals <- the_slots
glob_vals <- eventReactive(input$saver, {
set_new_vars <- list(input$new_var)
names(set_new_vars) <- input$new_var_name
the_slots <<- make_globs(new_var = set_new_vars)
lapply(list('new_var','new_var_name'),function(i)updateTextInput(session,i, value = ""))
return(the_slots)
})
output$envs <- renderPrint({
glob_vals()
})
output$sels <- renderUI({
vals <- 1:length(glob_vals())
Opts <- unlist(lapply(vals,function(i)sprintf('<option value="%s">%s</option>',i,names(glob_vals()[i])))) %>% HTML
HTML(
paste(
"<div class='shiny-input-container'>",
"<label class='control-label' for='the_ups'></label>",
"<div><select id='the_ups'>",Opts,"</select></div>",
"</div>",sep=""))
})
output$sel_vals <- renderPrint({
ref_cards <- lapply(1:length(glob_vals()),function(i)
data.frame(the_names = names(glob_vals()[i]),the_vals = glob_vals()[[i]]))%>%
rbind.pages
ref_cards[input$the_ups,'the_vals']
})
})
ui <- shinyUI(
bootstrapPage(
tags$div(class="container",
fluidRow(
tags$h4(HTML('These inputs will update the variable list \n like a variable in Sys.getenv()')),
column(6,textInput(inputId = "new_var_name",label = "variable name")),
column(6,textInput(inputId = "new_var",label = 'variable value'))
),
fluidRow(
column(6,
tags$h4(
HTML('Pressing the `add_new` button will load the variables and display the corresponding values below'),
actionButton(inputId = "saver",label = "add_new")
)),
column(6,tags$h4("You can even dynamically update a selection input with newly created paths or environment variables"),
uiOutput('sels'))
),
fluidRow(
column(6,verbatimTextOutput('envs')),
column(6,verbatimTextOutput('sel_vals')))
)))
shinyApp(ui,server)
}
And the result: