end of line sequences in different OS

end of line sequences
Windows end of line sequence:  \r\n
Unix end of line sequence: \n
Mac end of line sequence: \r

Recovering moved or deleted files in Linux

I was developing one C program which I spend 1 day writing with around  500 lines of code in Ubuntu 12.04 

for compiling in GCC, I used the below command

# gcc server.c -o server.c

instead of giving gcc server.c -o server 

now my whole source code was replaced with the binary file :( :(  , a simple mistake which caused my whole source code got deleted or replaced. I had a habit of pressing for auto completing the file names. 

After searching for some time googling, i got a solution which worked for me and saved my 9 hours of work.

I got the help form this below link

http://www.cyberciti.biz/tips/linuxunix-recover-deleted-files.html

repeating what is said there and which i tried and worked for me

in the console with sudo permission

sudo grep -a -B[size before] -A[size after] 'filename or unique content' /dev/[your_partition] > file.txt

-i : Ignore case distinctions in both the PATTERN and the input files i.e. match both uppercase and lowercase character.

-a : Process a binary file as if it were text

-B Print number lines/size of leading context before matching lines.

-A: Print number lines/size of trailing context after matching lines.

my command was

sudo grep -a -B10 -A1000 'UNIQUE_SERVER_IP' /dev/sda1 > file.txt

UNIQUE_SERVER_IP was the #define i did it in my source code. After the command is over, open the file.txt with vi or any text editor and search for the string 'UNIQUE_SERVER_IP'. you should find your source code around the string, copy paste and save to the required file name

I got the my source code back in some time.

counting number of lines in c and include files in Linux

After writing source code in Linux, if you want to count the number of lines in .c and .h files

find . -name '*.c' -o -name '*.h' | xargs wc -l

Converting IP Address from string in dot format to 32 bit integer

C program to convert IPv4 address from String formatted in dat notation like "10.0.0.1" to a 32 bit integer in Linux

#include<stdio.h>
#include <arpa/inet.h>

main()
{

    uint32_t ip;
    struct in_addr ip_addr;

    ip = inet_addr("10.0.0.1");
    printf("IP Integer: %d\n", ip);
    ip_addr.s_addr = ip;
    printf("The IP address is: %s\n", inet_ntoa(ip_addr));

}

Cassandra cqlsh queries

Below are the commands useful for querying the cassandra database .
These are executed by logging into the Cassandra command line interface(CLI), CQLSH

1) showing the keyspaces(or databases )

describe keyspaces;

2) Showing Tables in the keyspace(or database)

2.1. use <keyspace_name>;

2.2 describe tables;  this will show the tables in the keyspace(database)

3) Creating Index to an Exiting table with column

 CREATE INDEX tripid_idx ON table_4(tripid);


4) To show TABLE info using cqlsh
        DESC TABLE table_1 ;

Turning off expandtab in VIM for editing makefile

if you had set the .vimrc to change the tab to spaces for C programming, it will be difficult to edit or create makefiles,

 i had trouble creating makefile , i was getting the below error

Makefile:18: *** missing separator.  Stop.


after googled little and  found the  solution, edit the .vimrc file like below



let _curfile = expand("%:t")
if _curfile =~ "Makefile" || _curfile =~ "makefile" || _curfile =~ ".*\.mk"
set noexpandtab
else
set expandtab
set tabstop=4
set shiftwidth=4
endif

Using arrow keys in insert mode shows characters in vi editor

while using vi in Oracle virtual box with Ubuntu 12.04 as the guest OS with Windows 7 as the host, when we press arrow keys in insert mode, it used to print B, A, D, C

to fix this add the below line to the .vimrc file, if  it is no file create it

set nocompatible

after this setting if you open the vi , the problem should not come