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+Linux:Comparing Remote with Local
+=================================
+:author: Aaron Ball
+:email: nullspoon@iohq.net
+
+
+== {doctitle}
+
+Today I ran into quite the conundrum. I've been needing to compare the contents
+of a file on a remote server with the contents of a file on my local server
+over ssh. My original solution was to copy the file from one server to the
+other over sftp and compare their contents with diff.
+
+However, when you need to compare more than just the contents of a file, things
+can get really messy. Take for instance another situation where I needed to
+compare the contents of a directory. First, I needed to output the contents of
+a directory on BOTH servers into two files I had to create. Then I had to sftp
+into one server, copy it over to the other server, and run diff to compare
+their contents. Talk about complicated, yeah?
+
+All this copying and sftp-ing around frustrated me to the point where I wanted
+to find another solution. Sadly, my solution is a bit complicated for someone
+who doesn't know the linux command line super well, but at least it works and
+it works fast. I'll go slowly because if I don't, I won't get it myself either. 
+
+----
+ssh username@ServerIP 'ls -1 /tmp' | diff <(ls -1 /tmp)
+----
+
+Here's our example. The end result of this example is to get a comparison of
+the contents of a remote /tmp directory and the contents of our local /tmp
+directory.
+
+First things first, we have to run a command remotely to get the contents of
+said remote directory. To do this, we run simply
+
+----
+ssh username@ServerIP 'ls -1 /tmp'
+----
+
+That gets a list of the files and folders in the /tmp directory.  Specifically,
+the '-1' switch gives us one file or folder per line.
+
+Next up we pipe that into the diff command.
+
+For those of you who may not know about this functionality, piping basically
+takes the output of one command, and feeds it to another. In this case, we are
+taking the listed contents of a remote directory and feeding it to the diff
+command.  Now, we do this by using the following.
+
+----
+... | diff ...
+----
+
+Basically, the diff command works by finding the difference between the first
+thing it is given and the second thing it is given. Generally speaking, diff
+works like the following. 
+
+----
+diff <file1> <file2>
+----
+
+In this case we are saying diff which means to substitute what was piped in
+with the -.
+
+Up to this point, we have the contents of our remote directory and we have run
+the diff command. All we need now is to give it the second input to compare our
+first to. This brings us to our final step getting the contents of a local
+directory.
+
+This is about one of the most common linux command line functions performed.
+However, due to the fact that we want to compare the contents of the directory
+with the contents of another directory, things get a bit more complicated
+sadly. Do accomplish this, we need to run a nested command.
+
+Ordinarily running ls -1 /tmp after a diff command would result in an error
+rather than giving us what we want. To substitute a command for a file and so
+compare the command's output, we need to encase it in <().  Our final piece of
+the command should look like this.
+
+----
+<(ls -1 /tmp)
+----
+
+This completes our command. If you try to run the entire thing, you should be
+asked for your password to the remote server. Upon entering your password, the
+command should run as expected, comparing the files and folders in the two
+directories.
+
+The final command again looks like this...
+
+----
+ssh username@ServerIP 'ls -1 /tmp' | diff <(ls -1 /tmp)
+----
+
+If you want to get really tricky, you can compare the contents of a
+remote file and the contents of a local file. We'll take httpd.conf for
+instance. 
+
+----
+ssh username@ServerIP 'cat /etc/httpd/conf/httpd.conf' | diff <(cat /etc/httpd/conf/httpd.conf)
+----
+
+Hopefully that description wasn't too confusing. It's a complicated command to
+run (probably the worst I have ever used actually), but with some practice, it
+should become pretty easy if you understand how it works.
+
+Let me know if I didn't describe anything well enough and I will do my best to
+help out and update the post so it is more user friendly.
+
+Thanks for reading!
+
+
+Category:Linux
+Category:SSH
+
+
+// vim: set syntax=asciidoc: