抑制 R 中的 system() 输出

Question

I wanna apply the invisible() function behavior to an output I got in my script that goes like this system("cmd.exe", input = command) . However, even when using invisible, the output still shows in console. Is there any way to hide it?

EDIT: I'm running curl in the command to download a webpage and the output is the expected curl output.

EDIT2: Reproducible example

url <- "www.google.com"
command <- paste0('curl "', 
                  url,
                  '"',
                  ' -H "Pragma: no-cache" -H "Accept-Encoding: gzip, deflate, br" -H "Accept-Language: en-US,en;q=0.9" -H "Upgrade-Insecure-Requests: 1" -H "User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36" -H "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8" -H "Cache-Control: no-cache" -H "Cookie: uupid69991=eb4c8ec5-1f94-4cf5-957d-e477a778f79c; uupid99993=eb4c8ec5-1f94-4cf5-957d-e477a778f79c; uupid89991=1; uupid79991=Fee_Based_Role; locale=en; uupid99991=1903 x 1012; IVZSESSIONID=CEHrDvYqpDuQ-zwy8YZpWwm1RWZHY3DGq4V7elBfxcH87XFFo-J_^! -175310928; _ga=GA1.2.1974800928.1524362050; _gid=GA1.2.1544243785.1524362050" -H "Connection: keep-alive" --compressed',
                  ' > google.html')

invisible(system("cmd.exe", input = command))

Console Output:

Microsoft Windows [Version 10.0.16299.371]
(c) 2017 Microsoft Corporation. All rights reserved.

C:\Users\gonza\OneDrive\Documents\etfcmfa>curl "www.google.com" -H "Pragma: no-cache" -H "Accept-Encoding: gzip, deflate, br" -H "Accept-Language: en-US,en;q=0.9" -H "Upgrade-Insecure-Requests: 1" -H "User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36" -H "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8" -H "Cache-Control: no-cache" -H "Cookie: uupid69991=eb4c8ec5-1f94-4cf5-957d-e477a778f79c; uupid99993=eb4c8ec5-1f94-4cf5-957d-e477a778f79c; uupid89991=1; uupid79991=Fee_Based_Role; locale=en; uupid99991=1903 x 1012; IVZSESSIONID=CEHrDvYqpDuQ-zwy8YZpWwm1RWZHY3DGq4V7elBfxcH87XFFo-J_^! -175310928; _ga=GA1.2.1974800928.1524362050; _gid=GA1.2.1544243785.1524362050" -H "Connection: keep-alive" --compressed > google.html
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   231  100   231    0     0    982      0 --:--:-- --:--:-- --:--:--   982

Answer 1

Use intern=TRUE in your system call. From the system help page:

intern  
a logical (not NA) which indicates whether to capture the output of the command as an R character vector.

Once you do that you can either use invisible or just store the results to keep them from being printed.

Answer 2

You can use the sink function to divert output in R.

> curl::curl('https://stackoverflow.com/')
A connection with                                        
description "https://stackoverflow.com/"
class       "curl"                      
mode        "r"                         
text        "text"                      
opened      "closed"                    
can read    "yes"                       
can write   "no"                        
> sink(file="nul") # set file = '/dev/null' if using Unix-based OS
> curl::curl('https://stackoverflow.com/') # no output

If you set file to something else, it will print output to that file instead of the console.

Answer 3

Setting the "ignore.stdout" or "ignore.stderr" attributes (or both) to TRUE might work (may be specific to Unix operating systems). "ignore.stdout" suppresses messages written to "stdout" and "ignore.stderr" suppresses messages written to "stderr".

So:

system(some_command, ignore.stdout = TRUE, ignore.stderr = TRUE)