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I'm trying to print just the verbose sections of a cURL request (which are sent to stderr) from the bash shell.

But when I redirect stdout like this:

curl -v http://somehost/somepage > /dev/null

Some sort of results table appears in the middle of the output to stderr:

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0

Followed by this near the end:

{ [data not shown]
118   592    0   592    0     0  15714      0 --:--:-- --:--:-- --:--:-- 25739

Which makes the response headers less readable.

I don't see this text when not redirecting.


Another way to see the effects:

Table doesn't appear:

curl -v http://somehost/somepage 2>&1

Table appears:

curl -v http://somehost/somepage 2>&1 | cat

1) How come this shows up only with certain types of redirects?

2) What's the neatest way to suppress it?

Thank you

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4 Answers 4

up vote 14 down vote accepted

Try this:

curl -vs -o /dev/null http://somehost/somepage 2>&1

That will suppress the progress meter, send stdout to /dev/null and redirect stderr (the -v output) to stdout.

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5  
Thanks, -s was the key! –  Ian Mackinnon Aug 7 '10 at 17:59
1  
@IanMackinnon Note that with -s but without -v you will not see errors such as failure to connect. For that you should also add -S (or --show-error) as in mhoydis's answer. –  Artyom Apr 14 at 9:47

With reference to question 1 (how cURL knows to only display the table when output is redirected), I didn't realise a program could tell its outputs were being directed, but it seems on POSIX systems there is a function isatty which reports whether or not a file descriptor refers to a terminal.

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1  
Here's a Bash snippet: [[ -p /dev/stdout ]] && echo "stdout is to a pipe"; [[ -t 1 ]] && echo "output to terminal"; [[ ! -t 1 && ! -p /dev/stdout ]] && echo "output redirected" –  Dennis Williamson Aug 7 '10 at 20:41
curl --fail --silent --show-error http://www.example.com/ > /dev/null

This will suppress the status dialog, but will otherwise output errors to STDERR normally.

user@host:~# curl http://www.yahoo.com > /dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  254k    0  254k    0     0   403k      0 --:--:-- --:--:-- --:--:--  424k

The above outputs the status table when redirecting.

user@host:~# curl --fail --silent --show-error http://www.yahoo.com > /dev/null

The above suppresses the status stable when redirecting, but errors will still go to STDERR.

user@host:~# curl --fail --silent --show-error http://www.errorexample.com > /dev/null
curl: (6) Couldn't resolve host 'www.errorexample.com'

The above is an example of an error to STDERR.

user@host:~# curl -v --fail --silent --show-error http://www.errorexample.com > ~/output.txt 2>&1
user@host:~# cat ~/output.txt 
* getaddrinfo(3) failed for www.errorexample.com:80
* Couldn't resolve host 'www.errorexample.com'
* Closing connection #0
curl: (6) Couldn't resolve host 'www.errorexample.com'

Just add 2>&1 to the end to redirect STDERR to STDOUT (in this case, to a file).

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To put real error messages somwhere, you should write strerr into a log file. Something like that:

curl  "http://domain.name/process" --stderr /var/log/curl_err.log > /dev/null
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