Get Windows command to run through system/shell.exec

Question

I use the Windows command tree often to print out a tree diagram of the contents of files. I'd like to add this to my workflow in R but can't get the command to run though system or shell.exec and can't figure out why. Here is a reproducible example with 4 approaches and error messages using shQuote (with and without) in system and shell.exec command. When I use cat I can paste the command to the Windows command line manual (not using R) and the tree diagram is produced. What am I doing incorrectly that I can't make this run in R?

## build some mock files and directories with lapply
lapply(file.path("TEMP", c("", "X", "Y")), dir.create)
lapply(file.path("TEMP", paste0(c("A", "B"), ".txt")), file.create)

## create path to external file
out <- file.path(getwd(), "TREE.txt")

## create the tree command
cmd <- paste("tree", shQuote(file.path(getwd(), "TEMP")), "/f /a >", shQuote(out))
cat(cmd)  ## view it

system(cmd)  ## attempt 1

cmd <- paste("tree", shQuote(file.path(getwd(), "TEMP")), "/f /a >", shQuote(out))
shell.exec(cmd)  ## attempt 2

cmd2 <- paste("tree", file.path(getwd(), "TEMP"), "/f /a >", out)
system(cmd2)  ## attempt 3
shell.exec(cmd2)  ## attempt 4

cat(cmd, file="clipboard")


## > out <- file.path(getwd(), "TREE.txt")
## > cmd <- paste("tree", shQuote(file.path(getwd(), "TEMP")), "/f /a >", shQuote(out))
## > cat(cmd)
## tree "C:/Users/trinker/Desktop/TEMP" /f /a > "C:/Users/trinker/Desktop/TREE.txt"> 
## > system(cmd)
## Too many parameters - >
## > 
## > cmd <- paste("tree", shQuote(file.path(getwd(), "TEMP")), "/f /a >", shQuote(out))
## > shell.exec(cmd)
## Error in shell.exec(cmd) : 
##   'tree "C:/Users/trinker/Desktop/TEMP" /f /a > "C:/Users/trinker/Desktop/TREE.txt"' not found
## > 
## > 
## > cmd2 <- paste("tree", file.path(getwd(), "TEMP"), "/f /a >", out)
## > system(cmd2)
## Too many parameters - >
## > shell.exec(cmd2)
## Error in shell.exec(cmd2) : 
##   'tree C:/Users/trinker/Desktop/TEMP /f /a > C:/Users/trinker/Desktop/TREE.txt' not found

Answer 1

Use shell . On Windows, system does not use a shell (it only runs system commands). You're trying use a pipe to redirect output, thus you encounter the problem noted in ? system ? system :

command must be an executable (extensions '.exe', '.com') or a batch file (extensions '.cmd' and '.bat'): these extensions are tried in turn if none is supplied.) This means that redirection, pipes, DOS internal commands, ... cannot be used: see shell if you want to pass a shell command-line.