Tuesday, November 23, 2010

Recursive grep with filters - command line

you have a list o directories that you want to search a pattern BUT you want to exclude a few directories

use ls and grep recursive and apply a filter for the directory that you want to exlude

shell$ pwd
shell$ ls
work documents logs bin
# you want to search on all except logs for pattern 'invoice'

shell$ for i in `ls` ;do  if [ $i != 'logs' ]; then grep -r 'invoice' $i; fi; done
... output

what it happens is this:

the for loop executes based on the command `ls`
all the output is taken and feed it to the do
inside the do we are filtering off 'logs' (with the if) and then search for invoice with grep -r

Thursday, November 18, 2010

Vi(vim) column editing

In case that you want to edit by column and you use vi(vim) - this will do it.

To use it, press:

* Ctrl + V to go into column mode
* Select the columns and rows where you want to enter your text
* Shift + i to go into insert mode in column mode
* Type in the text you want to enter. You will see changes ONLY into the first row that you edit !
* Esc to apply your change (or alternately Ctrl+c)

You will now see your changed applied.

Ssh dynamic port(SOCKS) - firefox with different profiles

I have a data center network that is accessible only from a host - everything that is
behind it has to go trough it - this is usually what it happens to access  data centers and different solution being a site to site vpn (or road warrior - basically from your laptop to a firewall or access server).

I do deployments onto the servers that are behind this bastion host and I need to access the web applications ... how to do it ?!

Use openssh with a dynamic tunnel or putty (I use openssh) !

How to do it:

This is the diagram

/ web01 port 9000
me ---- internet ---- bastion_host --- web02 port 9001
                                     \ web03 port 9002
me$ ssh -v -D 8080 bastion_host

This has created a SOCKS proxy on my machine port 8080. If you don't know what is a SOCKS proxy - read on it http://en.wikipedia.org/wiki/SOCKS

Configure firefox to use a SOCKS proxy. Go to Edit -> Preferences -> Advanced -> Network -> Settings

Now you would like to use the browser to read as well your gmail or just surf the web -  so you need two different profiles

- one that uses the SOCKS proxy
- one for general use

To do so start firefox like this:

firefox -ProfileManager -no-remote

-no-remote is to start a separate process for firefox(which is not default)
-ProfileManager is to choose your profile - you can create a new one and from there take off the SOCKS proxy to use it for web surfing.

Now when you are into the profile with SOCKS proxy type in

http://web01:9000 and you have a direct connection !

Fire up a new firefox and choose the no proxy profile and just use it.

Thursday, November 11, 2010

Port redirect in linux to remote host

I had an application that needs to connect to a LDAP port (tcp:389) but the problem was that the LDAP was on an external network and on a non standard port (tcp:1389).
Pointing direct to remote_ip:1389 was not and option because the application is taking the LDAP port from the openldap libs (LDAP_PORT) which is a constant integer = 389 ...

The solution proved to be very simple - install a small port redirect program rinted do a small configuration into .

# config
/etc/rinetd.conf     389        remote_ip        1389

# start the daemon (only if you install it from rpm - if not just start manually)
/etc/init.d/rinetd start

And this is it - all works just fine.

Note that doing an iptables PREROUTING and DNAT will not work in my case because iptables can do
redirects ONLY into the local network.

Saturday, November 6, 2010

Delete empty lines into a file

Problem - you have a file that has a huge number of records and in between you have
empty lines.
This is my example.txt file:





To take the spaces off you have at least two simple tools to do it.
  • sed with this tool you can achieve your goal just by doing this - open a command line prompt and type the following
    linux$ cat example.txt | sed -e '/^$/d' you will see on your screen the following
  • grep with this we use a trick saying that we don't want certain patterns from the file - the empty lines - open a command line prompt and type the following
    linux$ grep -v '^$' example.txt
  • asd