Monday, October 8, 2012

Stealth cURL

I use curl all the time, almost every day. Unfortunately curl thinks its a good idea to use their own user agent string when grabbing content from sites. This has the problem because sometimes devs code in exceptions for different browsers, so the page you get back for internet explorer is different than the one you get for firefox. Luckily, the curl devs included the ability to change your user agent string to whatever you want.

normally curl's agent string is this: (curl from my macbook)
User-Agent: curl/7.24.0 (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8r zlib/1.2.5

That is grabbed directly from the header that is sent to the server (captured using netcat). As you can see its fairly obvious that the person is on mac and they are using curl. To change this user agent agent so it appears as if firefox is grabbing it, we use the -A option. First we grab the valid user agent string we decide to use from In this case i'm going to use the latest firefox one, the command line is as follows:

curl -A 'Mozilla/5.0 (Windows NT 6.1; rv:15.0) Gecko/20120716 Firefox/15.0a2'
Now if you look at your logs, you will see the user-agent string will reflect the new string.

curl supports config files using -K, so you can just place it in a file along with whatever else you want to use and reference the config files, a nice example is in the man page.

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