Reference

Introduction
callr	Call R from R
Run R
r() r_safe()	Evaluate an expression in another R session
r_copycat()	Run an R process that mimics the current R process
r_vanilla()	Run an R child process, with no configuration
Run R in the background
r_bg()	Evaluate an expression in another R session, in the background
r_process	External R Process
r_process_options()	Create options for an r_process object
Persistent background R session
r_session	External R Session
r_session_options()	Create options for an r_session object
r_session_debug	Interactive debugging of persistent R sessions
Run R CMD
rcmd() rcmd_safe()	Run an R CMD command
rcmd_copycat()	Call and R CMD command, while mimicking the current R session
rcmd_safe_env()	rcmd_safe_env returns a set of environment variables that are more appropriate for rcmd_safe(). It is exported to allow manipulating these variables (e.g. add an extra one), before passing them to the rcmd() functions.
Run R CMD in the background
rcmd_bg()	Run an R CMD command in the background
rcmd_process	External R CMD Process
rcmd_process_options()	Create options for an rcmd_process object
Run Rscript
rscript()	Run an R script
Run Rscript in the background
rscript_process	External Rscript process
rscript_process_options()	Create options for an rscript_process object
Miscellaneous utilities
default_repos()	Default value for the repos option in callr subprocesses
supported_archs()	Find supported sub-architectures for the current R installation
Re-exported functions
reexports	Objects exported from other packages