Assign Values Passed at the Command Line or Interactively

Assign values to names in the working environment. The values are typically supplied through the command line, but can be supplied interactively.

Specifying the inputs and outputs of scripts through the command line can contribute to safter, more modular workflows.

cmd_assign_quiet() is identical to cmd_assign(), but does not print progress messages to the console.

Usage

cmd_assign(...)

cmd_assign_quiet(...)

Arguments

...

Name-value pairs.

Value

cmd_assign() is called for its side effect, which is to create objects in the global environment. However, cmd_assign() also invisibly returns a named list of objects.

Types of session

cmd_assign() behaves differently depending on how it whether it is called

1. interactively, or

2. inside an R script that is run from the command line.

For instance, if the code

cmd_assign(use_log = TRUE)

is run interactively, it creates an object called use_log with value TRUE.

But if the same code is run inside a script via the command

Rscript tidy_data.R --use_log=FALSE

it creates an object called use_log with value FALSE.

cmd_assign() is typically called interactively when a workflow is being developed, and through the command line when the workflow has matured.

Matching names and values

When used in a script called from the command line, cmd_assign() first matches named command line arguments, and then matches unnamed command line arguments, in the order in which they are supplied.

If, for instance, the script person.R contains the lines

cmd_assign(.data = "raw_data.csv",
           max_age = 85,
           .out = "person.rds")

and if person.R is run from the command line using

Rscript person.R raw_data.csv person.rds --max_age=100

then cmd_assign() first matches named command line argument --max_age=100 to cmd_assign() argument max_age, and then matches unnamed command line arguments raw_data.csvandperson.rdstocmd_assign()arugments.dataand.out`.

Coercing values passed at the command line

Values passed at the command line start out as text strings. cmd_assign() coerces these text strings to have the same class as the corresponding values in the call to cmd_assign(). For instance, if a script called fit.R contains the lines

cmd_assign(.data = "cleaned.rds",
           impute = TRUE,
           date = as.Date("2026-01-01"),
           .out = "fit.rds")

and if fitted.R is run from the command line using

Rscript fitted.R cleaned.rds fit.rds --impute=TRUE --date=2025-01-01

then cmd_assign() will create

• a character vector called .data with value "cleaned.rds",

• a logical vector called impute with value TRUE,

• a date vector called date with value "2025-01-01", and

• a character vector called .out with value `"fit.rds".

References

• Command-Line Programs Introduction to Rscript

See also

• extract_shell() Turn a cmd_assign() call into a shell command

• extract_make() Turn a cmd_assign() call into a Makefile rule

• shell_script() Create a shell script

• makefile() Create a Makefile

• Quick Start Guide How to use cmd_assign()

• Modular Workflows for Data Analysis Safe, flexible data analysis workflows.

• Base R function commandArgs() uses a more general, lower-level approach to processing command line arguments. (commandArgs() is called internally by cmd_assign().)

• littler Alternative to Rscript

Examples

if (interactive()) {
  cmd_assign(.data = "mydata.csv",
             n_iter = 2000,
             .out = "results.rds")
}