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Old 08-09-2016, 08:38 PM   #1
dumblinuxuser
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cURL command clarification


Hello All,

Can you please help me understand what does cURL -D- command does. My knowledge around curl is pretty basic and at work I was provided a curl command that looks like below, I understand most of the options by reading the man page but the minus behind D is what I am unable to understand.
Can somebody explain in plain terms as to what that minus (-) means

curl -k -D- -u <username>:<password> "https://url"

Thanks in advance.
 
Old 08-09-2016, 08:49 PM   #2
Beads
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Quote:
Originally Posted by dumblinuxuser View Post
Hello All,

Can you please help me understand what does cURL -D- command does. My knowledge around curl is pretty basic and at work I was provided a curl command that looks like below, I understand most of the options by reading the man page but the minus behind D is what I am unable to understand.
Can somebody explain in plain terms as to what that minus (-) means

curl -k -D- -u <username>:<password> "https://url"

Thanks in advance.
Hello! The -D option means "Dump Header". Here is the official explanation:

Write the protocol headers to the specified file.

This option is handy to use when you want to store the cookies that a HTTP site sends to you. The cookies could then be read in a second curl invoke by using the -b/--cookie option!

When used on FTP, the ftp server response lines are considered being "headers" and thus are saved there.

If this option is used several times, the last one will be used.
 
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Old 08-09-2016, 09:01 PM   #3
dumblinuxuser
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Thank you Beads. The man page did tell me about the -D option, can you tell me what does the (-) on the right side mean "-D-" is there a significance for that "-" coz, when I remove it the cURL command is failing with error

curl: (6) Couldn't resolve host 'username:<passowrd>'
so i am thinking the that minus (-) on right side is somehow contributing to the -u option to be read correctly.

Last edited by dumblinuxuser; 08-09-2016 at 09:04 PM.
 
Old 08-09-2016, 10:09 PM   #4
AwesomeMachine
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I think it's a typo.
 
Old 08-09-2016, 10:28 PM   #5
norobro
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From the bash man page:
Quote:
--
A -- signals the end of options and disables further option processing. Any arguments after the -- are treated as filenames and arguments. An argument of - is equivalent to --.
Try your command this way:
Code:
curl -k -u <username>:<password> "https://url" -D
 
Old 08-09-2016, 10:33 PM   #6
CDR255
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The `-D` option to curl takes a filename as an argument.

That is, You need to type `curl -D <file>` for it to store the header in the <file>.

In *nix OSes, the `-` character is a special case. When used in place of a file, it tells the program to write to the standard output (STDOUT).

Typing `curl -D-` is telling curl to write the headers to the standard output.

Removing the `-` in your example makes curl think You want to save the headers in a file named `-u`. This makes curl think You are trying to visit the url <username> at the port <password> (Because you would write it <url>:<port> if that is what you wanted to do.)

There is probably a file in Your present working directory named `-u` that you can safely delete. If you type a filename after the -D option, the error should go away.

Code:
curl -k -D foo -u <username>:<password> "https://url"
(My own assumptions here, obviously. YMMV.)

Last edited by CDR255; 08-09-2016 at 10:42 PM. Reason: Adding in example
 
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Old 08-09-2016, 10:42 PM   #7
dumblinuxuser
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Thank you CDR255, your explanation makes sense. Let me try what you have suggested.
 
  


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