OpenPeta

You have 100 photos which was captured by using your 5 MP digital camera.Each Image has occupied 4 MB in your memory card and also You want to upload all the files into picasa or facebook or an other social networking sites. But the maximum image uploading size is 1 MB in those websites. So it is very difficult to reduce the size of each and every photo using some photo editing softwares. In this situation you can use the following shell script to convert or compress more than one images. Let us assume, the photos are available in /home/photos folder.

# cd /home/photos
# vim compress.sh

1
2
3
4

for img in `ls *.JPG`
do
convert -quality 40% $img my-$img
done

or
Simply copy the script and paste into your image folder. and run the script in your terminal

# chmod 777 compress.sh
# ./compress.sh

This script will reduce the size of image into approximately 300 KB .
Reference : IBM Website

Running C and C++ applications in Linux is entirely different from Windows TurboC++ users. Linux uses GCC [Gnu Compiler Collections - C and C++ compiler] for developing these applications . Let us see how to develop C and C++ applications in Linux .

Checking GCC compiler
GCC comes with all Linux flavors by default . To check the version of your GCC , type this command in your terminal

root@Ubuntu:/home/anthoniraj# gcc  –version
gcc (Ubuntu 4.4.1-4ubuntu9) 4.4.1
Copyright (C) 2009 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

By default only C compiler will be there in GCC , you can install C++ support by typing this command in Ubuntu

#sudo apt-get install build-essential

Developing C Program
You can use your favorite editor or IDE like Netbeans or Eclipse to develop the C and C++ programs. I am using VIM the simple and king of all editor for developing these programs. Now simply we can write one C program for finding factorial of a given number.
#vim factorial.c [ file type is .c ]

#include<stdio.h>
int main()
{
int n , i ;
unsigned long int  res = 1;
printf("\nEnter the number to find the factorial:");
scanf("%d" , &n );
for(i = 1 ; i <= n ; i++)
{
res *= i;
}
printf("\n The factorial value of %d is %lu\n" , n, res);
return 0;
}

Compiling and Running
To compile c program , use gcc with file name

#gcc factorial.c
#./a.out [Default buffer for output]
Enter the number to find the factorial: 5
The factorial value of 5 is 120
or
#gcc factorial.c -o fact.out
#./fact.out [customized file for output]

Note :

1. There is no void keyword in GCC ,
2. Use int instead of void and also use return 0 .

Developing C++ Program
Now I am going to write C++ for the same factorial method.
#vim factorial.cpp [File Type is cpp]

#include <iostream>
using namespace std;
int main()
{
int n ;
unsigned long int  res = 1;
cout << "\nEnter the number to find the factorial:" << endl;
cin << n ;
for(int i= 1 ; i <= n ; i++)
{
res *= i;
}
cout <<"The factorial value of " <<"is " << endl;
return 0;
}

Compiling and Running
To compile c program , use gcc with file name

#g++ factorial.cpp
#./a.out [Default buffer for output]
Enter the number to find the factorial: 5
The factorial value of 5 is 120
or
#g++ factorial.cpp -o fact.out
#./fact.out [customized file for output]

Note :

1. Dont use .h for header files
2. Use name space for header-file functions

ls – List Directories and Files
ls command will display the files and folders of current working directory. You can use some options to utilize this command effectively.
1. Display files and folders

anthoniraj@Ubuntu:~/sample$ ls

sam.txt  uploads  users.csv  users.txt

2. Display the file and folder with privileges , ownership , and size

anthoniraj@Ubuntu:~/sample$ ls -l
total 16
-rw-r–r– 1 anthoniraj anthoniraj    5 2010-04-08 06:49 sam.txt
drwxrwxrwx 2 anthoniraj anthoniraj 4096 2010-03-26 08:49 uploads
-rw-r–r– 1 anthoniraj anthoniraj  140 2010-04-07 10:33 users.csv

-rw-r–r– 1 anthoniraj anthoniraj  145 2010-04-07 10:32 users.txt

3. Display all files including hidden files

anthoniraj@Ubuntu:~/sample$ ls -a
.  ..  sam.txt  uploads  users.csv  users.txt

ls command output

4. Display the folder content recursively

anthoniraj@Ubuntu:~/sample$ ls -R

.:

sam.txt  uploads  users.csv  users.txt
./uploads:

cs1999.pdf  kavidhai.pdf  New Text Document.txt  Sample.txt

5. Display the inode or index number of each file

anthoniraj@Ubuntu:~/sample$ ls -i
331894 sam.txt  336568 uploads  331901 users.csv  331902 users.txt

One of the powerful feature of Linux Shell is the help page for commands. all commands comes with the manual page so that it can be easily understood by user.For accessing help or syntax details about any command in Linux , simply get into the terminal and type

# man command-name

This will display the information like name , syntax , description , example , author of the particular command. User can also use some options like  “-f” for short description and “-k” for displaying commands based on the keyword.
Regular Usgae
1. Displaying Manual or Help Page

#man find

Manual Page for Find Command

2. Getting Short Description

#man  -f  ifconfig

Short Description of ifconfig

3.Getting List of commands using Keyword
If you want to know about the commands for network operations ,  you do not know all the Linux networking commands , In this situaltion “man -k” option will help you. Type the keyword “network” with option “-k” in man command , it will display all the commands matching the keyword like network.

#man -k “network”

List of Network Commands

4. Converting Manual Page into Portable Format [ Text , PDF , PS ]

The default format of the man pages are in troff [ Text Formatting System]. We can convert troff format to text pdf or ps format using man with following options
i) For Text File conversion

# man ls | col -b > lstext.txt

ii) For PDF or PS conversion

#man -t ls > lsps.ps
#man -t ls | ps2pdf – > lstext.pdf