capture subprocess output but print nothing to console?

Question

I'm trying to run a curl command using subprocess. Works fine. I've got the output I need in a variable. The onlything I want is when the process runs, I don't want this printing in the console:

 % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 255 100 153 100 102 56 37 0:00:02 0:00:02 --:--:-- 56

Here's what that part of the script looks like:

 import subprocess def F_createSingleTable(table_name): un = "test" pw = "testpass" url = "https://blah.fake.url.com:7877/services/createstable" size = "10" size_til_archive = "30" retention = "5" curl_call =\ [\ 'curl', \ '-k', \ '-u', \ (un)+":"+(pw), \ (url), \ '-d', \ 'name='+(table_name), \ '-d', \ 'size='+(size), \ '-d', \ 'size_til_archive='+(size_til_archive), \ '-d', \ 'retention='+(retention)\ ] process = subprocess.run((curl_call), check=True, stdout=subprocess.PIPE, universal_newlines=True) output = process.stdout if "already exists" in (output): print("table: "+(table_name)+" already exists")

if it matters the actual response I get which is stored in output is this:

 <?xml version="1.0" encoding="UTF-8"?> <response> <messages> <msg type="ERROR">table_name table already exists</msg> </messages> </response>

I don't need to save it, just check if 'alredy exists" is in it. Which I have and works.

Thanks

NOTE: I was originally wanting to use subprocess.call but I couldn't seem to capture the output to check if already exists was in the response

See here: unix.stackexchange.com/questions/196549/hide-curl-output — Jan
– Jan, Commented Jan 11, 2020 at 0:42
Why are you using curl when Python has its own module for performing HTTP requests? — Barmar
– Barmar, Commented Jan 11, 2020 at 0:45
@Dan D. - dammit. what a "duh" response. Adding -s solved what I wanted. thanks — CSA
– CSA, Commented Jan 11, 2020 at 0:54
@Barmar I tried with requests originally. Wasnt sure how to build the call with it so i reverted to curl in the os — CSA
– CSA, Commented Jan 11, 2020 at 0:57

manveti · Accepted Answer · 2020-01-11 00:53:28Z

What you're seeing on the console is on stderr, not stdout. In it's normal mode, curl prints the fetched content to stdout and the transfer stats to stderr. You can either suppress the statistics with the -s/--silent flag or discard stderr by passing stderr=subprocess.DEVNULL to your subprocess call.

If you care about the stderr output, you can also capture it separately by passing stderr=subprocess.PIPE or merge it into the stdout stream (obviously not recommended for the specific use case in the question) by passing stderr=subprocess.STDOUT.

yeah. -s to the original curl command solved it as per dan d's comment. i haven't slept... I shoulda thought of that. Though there are commands I run sometimes where the app isn't common and doesnt have a suppress built in, so it would be nice to do it at the subprocess level as well. I'll test this out too for my own knowledge growth.

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