print every nth line

Some time back I was working with lot of data and wanted to analyze only the every 10 line sometimes and sometimes every 20th line. I had to keep doing these changes in vim or otherwise so finally I wrote a program to do this for me. If you need such a program then here it is:

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      #!/bin/bash -<br /> #===============================================================================<br /> #<br /> #          FILE:  print_nth_line.sh<br /> #<br /> #         USAGE:  ./print_nth_line.sh<br /> #<br /> #   DESCRIPTION:  Print every nth line<br /> #<br /> #       OPTIONS:  ---<br /> #  REQUIREMENTS:  ---<br /> #          BUGS:  ---<br /> #         NOTES:  ---<br /> #        AUTHOR:   (),<br /> #       COMPANY:<br /> #       VERSION:  1.0<br /> #       CREATED:  12/08/2010 05:36:53 PM IST<br /> #      REVISION:  ---<br /> #===============================================================================<br /> <br /> if [ x"$1" == "x" ]<br /> then<br /> echo "Please provide the line numbers to print .. .ex 3 will print 3,6,9"<br /> exit -1;<br /> fi<br /> if [ x"$2" == "x" ]<br /> then<br /> echo "Please provide the filename"<br /> exit -2;<br /> fi<br /> awk 'temp++ { if ( temp % '$1' == 0) print $1};' $2
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/bash debugger

9.2. A bash Debugger

In this section we’ll develop a very basic debugger for bash.[10] Most debuggers have numerous sophisticated features that help a programmer in dissecting a program, but just about all of them include the ability to step through a running program, stop it at selected places, and examine the values of variables. These simple features are what we will concentrate on providing in our debugger. Specifically, we’ll provide the ability to:

Using ssmtp to send mail using gmail.

First install the package ssmtp using the command:

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      sudo yum install ssmtp
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Open the configuration file for ssmtp as root user:

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      vim /etc/ssmtp/ssmtp.conf
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Make the following changes to the configuration file:

root=**username**@gmail.com
mailhub=smtp.gmail.com:587
hostname=**username**@gmail.com
UseSTARTTLS=YES
AuthUser=username
AuthPass=password
FromLineOverride=yes

In order to make the default (root) “from” field be the server name,
edit the /etc/ssmtp/revaliases file as root user :

using gnuplot for time plotting

Couple of days back, I was working with some data and wanted to plot it. I had couple of options Excel, ploticus and then our own gnuplot. My choice here was gnuplot, as this is most commonly available and helps me write scripts that can automate my repetitive task. So far, so good. The data I was plotting was against time, that was the problem. Couple of quick searches did not result into any luck to get me on the path and hence with some man pages and some documentation, finally I found this, might be this will be helpful for others.

vino – connect to running GNome session like RDP

One thing that all of us Linux users have probably missed is connecting to the running GNome session to see what is going on in the running session. This can be quite handy in couple of situations:

1. Debugging remote sessions – where you do not want a new session, instead want to connect to running session.

2. Maintaining running session from another PC. If you are running some applications on some Linux box and want to gracefully stop it using some commands other than kill -9 then it is best that you connect to the running session, if you are not using screen.

   Continue reading

Ranking of the most frequently used commands

Lets take a quick look at how to get the most frequently used commands on you shell. So what we need to do is this:

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      history | awk '{print $2}' | awk 'BEGIN {FS="|"}{print $1}' | sort | uniq -c | sort -n | tail | sort -nr
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So, how did we arrive at this and will this always work? No it might not always work. A typical example is where HISTTIMEFORMAT variable is set. In that case, if you check history, you will see that after the number column we have time and date in the specified format, in which case, you will get wrong information from the above command. Anyways, forgetting these special cases, lets go to how we got this command:

bash mathematical calculators.

To start with , the most simple and easy to use should be “bc”. but just for some guys who want to be more experimental, here are few more bash calulator programs. These are completely command line and thus you can completely integrate them in your shell script or use them in shell script to do some really crazy maths calculations.

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      sudo yum install calc clac
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Lets start with installing these. Before we start, don’t blame and flame me if your favourite is not there in the list. If it is not, better is you drop me  a comment or email, and I will see, if I can include it in the list above, but remember this is only for console based calculators.