Quick post on using diff to compare two directories in Linux. This will show the list of files and subdirectories that are different in either directories
[code]diff /PATH_TO_FIRST_DIRECTORY /PATH_TO_SECOND_DIRECTORY -r –brief [/code]
Options used
If you want to grep for certain http response codes in a apache log file
Details of the options
tells grep to look for space or tab before the specified string, which in this case is 200.
Simple one liner to check if your web server is using strong ciphers
[code]
openssl s_client -cipher LOW -host SERVER_NAME -port 443 [/code]
Simple script in python to look for credit card numbers in a file.
[code]
#Importing modules
import re
import os
# Define variables
inputFile = ‘test.txt’
searchPattern = ‘((\D(6011|5[1-5]\d{2}|4\d{3}|3\d{3})\d{11,12}\D)|(^(6011|5[1-5]\d{2}|4\d{3}|3\d{3})\d{11,12}\D))’
tempinputFile = open(inputFile)
tempLine = tempinputFile.readline()
while tempLine:
print ("LINE: " + tempLine)
foundContent = re.search(searchPattern,tempLine, re.IGNORECASE)
if foundContent:
print("FOUND: " + foundContent.group())
tempLine = tempinputFile.readline()
tempinputFile.close() [/code]
The script started out as a simple check for any 16 digit numbers that had a non numeric character on either end. But I tweaked it a little bit to look for credit card like numbers using the regex from http://www.regular-expressions.info/creditcard.html. Finally I added an option to match credit card like numbers if the numbers start at the beginning of the line (i.e there is no non-numeric number before the credit card number)
If you are every looking to match strings as a whole word instead of literal strings using a regular express, Word Boundaries are your friend
For example if you are looking to match a string of 10 numbers in a log file, you can use
[code]grep -i ‘\b[0-9]\{10,\}\b’ –color -H -n FILE_NAME_TO_SEARCH [/code]
The \b is the option that tells grep to look for a word character.
More information about the option is available at http://www.regular-expressions.info/wordboundaries.html
Use the following option to check out how network (NFS) shares are performing on your sever
[code]iostat -n 2[/code]
The -n option tells iostat to just show the network shares
2 tells iostat to refresh the stats every 2 seconds
Want your terminal to look like this? 
In addition to the coolness, factor it also helps you do (monitor) multiple things at a time. In this screenshot
You can achieve this by using the nifty screen utility. Screen allows you to multiplex between multiple consoles. So you can open one terminal and have multiple consoles on it. The commands for using screen are a bit hard to get used to. Here are the shortcuts I used to achieve the screen above
[code]c[/code]
[code] Shift + s [/code]
[code]Shift + a[/code]
As you might have figured out by now, “ctrl + a” puts you into screen command mode. You can get a list of all available options by executing
[code]ctrl +a[/code]
[code]?[/code]
Here’s a quick reference guide that has more details http://aperiodic.net/screen/quick_reference
Have fun multitasking 🙂
It looks like I was able to accomplish writing the application that I wanted to on the App Engine in 2 days!! at least in it’s basic form. After some help from Google, I updated the application I created yesterday (http://samurai-apps.appspot.com/) to display the User Agent string being sent by the client.
The code has been updated to github at https://github.com/kudithipudi/google-app-engine/
Lessons from day 2?
Next, I will try to pretty it up a bit.
Isn’t it amazing that I was able to create a simple app in a matter of 2 days and host it on an “infinitely” scalable platform without even taking our my credit card.
Phew.. that was a long title :). Was running into an issue with the setup shown in the picture below 
When we try to access the web site using https, the html content being served back was showing the app server name as the reference, rather than the web site.
So in this example, let’s say the web address was kudithipudi.org and the app server was app-server-kudithipudi, the HTML content was showing https://app-server-kudithipudi:8080 as the source.
Here’s how, we fixed it.
Edit the server.xml file found in $JBOSS_HOME/server/$JBOSS_PROFILE/deploy/jboss-web.deployer and update the HTTPS connector to use the web address (kudithipudi.org) as the proxyName.
BEFORE
[code]<Connector port="8443" protocol="HTTP/1.1" SSLEnabled="true"
maxThreads="250" scheme="https" secure="true"
clientAuth="false" sslProtocol="TLS"
keystoreFile="/opt/jboss/jboss-as/server/kudithipudi/conf/ssl/kudithipudi.keystore"
keystorePass="xxxxxx" />
[/code]
AFTER
[code]<Connector port="8443" protocol="HTTP/1.1" SSLEnabled="true"
maxThreads="250" scheme="https" secure="true"
clientAuth="false" sslProtocol="TLS"
proxyName="kudithipudi.org" proxyPort="443"
keystoreFile="/opt/jboss/jboss-as/server/kudithipudi/conf/ssl/kudithipudi.keystore"
keystorePass="xxxxxx" />
[/code]
For my own notes.. if you are using grep to parse through the contents of a file and want to see the preceding or proceeding content than the line that matched your query, you can use the following options
preceding content [code]grep -B NUMBER_OF_LINES_TO_DISPLAY query filename[/code]
for example, if I was searching for kudithipudi in a file names access.log and want to see 2 lines prior to the match, I would use [code]grep -B 2 kudithipudi access.log[/code]
proceeding content[code]grep -A NUMBER_OF_LINES_TO_DISPLAY query filename[/code]
for example, if I was searching for kudithipudi in a file names access.log and want to see 2 lines after the match, I would use [code]grep -A 2 kudithipudi access.log[/code]
preceding and proceeding content[code]grep -C NUMBER_OF_LINES_TO_DISPLAY query filename[/code]
for example, if I was searching for kudithipudi in a file names access.log and want to see 2 lines before and after the match, I would use [code]grep -C 2 kudithipudi access.log[/code]
