Check for linearity using a dynamic variable by a shiny widget

I want to use every time a different variable to put inside the plot() function to check for linearity using a shiny widget but I get: variable lengths differ (found for 'input$var')

## app.R ##
library(shiny)
library(shinydashboard)
library(shinyjs)
library(htmlwidgets)

ui <- dashboardPage(
  dashboardHeader(
    title="Task Managers' Workload Analysis",
    titleWidth = 400
    
  ),
  dashboardSidebar(
    selectInput("var","Select variable",choices = colnames(diamonds),selected = colnames(diamonds)[1])
  ),
  dashboardBody(
    plotOutput("hist")
  )
)

server <- function(input, output,session) {
  output$hist<-renderPlot({
    plot(price ~ input$var, data=diamonds)
  })
} 

shinyApp(ui, server)

>Solution :

You could either:

plot(eval(parse(text = input$var)) ~ price, data = diamonds)

or

plot(diamonds[[input$var]] ~ price, data = diamonds)