Terminal Emulator

Apps are great, but sometimes it is helpful to explore the MDI server from the command line. In keeping with the “in-app” MDI experience, the apps framework offers a simple terminal emulator, i.e., command terminal, that can be attached to UI elements.

The emulator is based on the R system command and is not meant to be a complete replacement for a proper, external command terminal when heavy developer use is needed. The in-app terminal is best for “poke and peek” tasks.

Although the terminal emulator is mostly targeted to developers, it is available to all users in local and remote modes. It is disabled on public servers for obvious reasons.

Do not confuse the R Console with the Command Terminal. The former executes commands in R, the latter executes commands on the host operating system.

Create a terminal emulator UI link

Terminal emulators can be launched from any server function as needed, but the typical usage is to create a link within your module’s UI function:

# myModule_ui.R
if(!serverEnv$IS_SERVER) commandTerminalLink(id = ns('terminal'), class = "my-class")
else ""

that shows the terminal emulator via your module’s server function with the icon is clicked:

# myModule_server.R
if(!serverEnv$IS_SERVER) observeEvent(input$terminal, {
    req(!serverEnv$IS_SERVER)
    showCommandTerminal(
        session,
        ... # see docs below
    )  
})

Note that it is appropriate to reinforce the suppression of terminals on public servers, although the underlying module will only load in local and remote modes.

Using the showCommandTerminal load function

The terminal itself appears in a stateful modal dialog, where ‘stateful’ means that the terminal will return to the same state when the same icon is clicked a second time.

As a dialog element, the terminal emulator does not follow the typical UI+Server pattern, instead, it is launched via the showCommandTerminal() function:

# commandTerminal_utilities.R
showCommandTerminal <- function(
    session, 
    host = NULL, 
    pipeline = NULL,
    action = NULL,
    runtime = NULL,
    dir = NULL, 
    forceDir = FALSE,
    tall = FALSE,
    wide = FALSE
)

where:

• session = the session object of the calling server function
• host = the host to ssh into when running terminal commands
• pipeline = as used in ‘mdi shell --action --runtime '
• action = see pipeline
• runtime = see pipeline
• dir = the suggested directory in which to open the terminal
• forceDir = always use dir, even if there is a cached value
• tall = whether the dialog is currently extra tall
• wide = whether the dialog is currently extra wide

Typical usage for many apps would set only the dir argument, the others are mainly for the Pipeline Runner app.

Additional references

For complete details, see:

• mdi-apps-framework : command terminal emulator