QR code: GUI tool for encoding decoding QR codes in linux

In the post "QR code: Encode and Decode QR code on linux command line" we saw usage of a command based tool to create QR codes in linux. Let us have a look at a GUI based tool for the same.

QTQR is gui a tool to create QR (Quick Response) code. We will need to install the tool qtqr

$ sudo apt-get install qtqr

Once installed we can launch the tool from GUI in debian under Applications->graphics->QTQR



We can launch it from terminal using the command qtqr

This will launch a window as shown below.



To create a QR code we can choose what kind of string we want to encode using the pull down menu at the left top as shown below.



Once selected we can enter the text in the text below at the left and then click on "save QR code" at the right bottom and save the QR image.



The QR image for the text "Hello" would look as below.



To decode a QR code using QTQR click on decode at the right corner. While selecting decode we can either choose a file or choose an image being viewed by a webcam. To test the decode, point to the same QR image of "hello" that we created above and click on open.



As we can see the tool has correctly decoded the image.

Useful links
http://code.google.com/p/qtqr/
http://en.wikipedia.org/wiki/QR_code

QR code: Encode and Decode QR code on linux command line

QR(Quick response) code as defined by google is

A machine-readable code consisting of an array of black and white squares, typically used for storing URLs or other information for reading by the camera on a smartphone.

Here is how we can create QR code in linux using command line.

Using command line:

To create QR code using command line we will need to install the package libqrencode3

$ sudo apt-get install libqrencode3

After successful install of the package we can encode any string of characters, text,url,numbers, into a QR code as shown below.

$ qrencode "string" -o "output file name"

Let us say we want to encode the string "Hello" into a QR code.

$ qrencode Hello -o hello

This will creat a hello.png file in the QR format as shown below.

To be able to decode a QR code on the command line we can use the package zbar.

$ sudo apt-get install zbar-tools

Once the package is installed we can use the command zbarimg to read a QR encoded file

$ zbarimg "image file name"

To decode the hello.png QR we created above

$ zbarimg hello QR-Code:Hello scanned 1 barcode symbols from 1 images in 0.05 seconds

Thus we can see that the QR-Code has been correctly recognized as "Hello "

Useful links: http://en.wikipedia.org/wiki/QR_code http://zbar.sourceforge.net/

Answers to Linux Quiz on semaphores

Answers to Quiz on linux Semaphores

1. Race condition occur when
Ans. There is uncontrolled access to shared data

2. The code that is surrounded by a semaphore is termed as
Ans. Critical section

3. To use a semphore as a mutex, semaphore needs to be initalized to the value of
Ans. 1

4.Which of the following will declare and initialize a mutex
Ans. DECLARE_MUTEX

5. The value of the mutex when it is locked by a process is
Ans. 0

6.To create a semaphore which will attempt to get the lock only once, we can use the function

Ans. down_trylock()
7. The functions down and down_interruptible work in similar fashion

Ans. False

8. The function call to release a semaphore is
Ans. up

9. A reader writer semaphore allows
Ans. Multiple readers or only one writer

10. Sending a signal from one thread to other regarding completion of a task/job can be done optimally using
Ans. Completion

Linux Quiz on semaphores

Quiz on linux Semaphores

1. Race condition occur when

There is uncontrolled access to data
There is uncontrolled access to shared data
Every time kernel accesses user space data
Every time user communicates with kernel


2. The code that is surrounded by a semaphore is termed as

Critical section
Sema section
Zero section
Muted section


3. To use a semphore as a mutex, semaphore needs to be initalized to the value of

0
1
-1
2


4. Which of the following will declare and initialize a mutex

DECLARE_MUTEX
SEMA_INIT_MUTEX
DECLARE_SEMA
MUTEX_CREATE


5. The value of the mutex when it is locked by a process is

0
1
-1
2


6. To create a semaphore which will attempt to get the lock only once, we can use the function

down()
down_tryonce()
down_trylock()
down_interrupt()


7. The functions down and down_interruptible work in similar fashion

True
False
Depends on kernel version
In case of mutex they are same


8. The function call to release a semaphore is

up
up_trylock
up_interruptible
All of the above


9. A reader writer semaphore allows

Multiple readers or only one writer
Multiple writers or only one reader
Multiple readers and writers
Only one reader or writer


10. Sending a signal from one thread to other regarding completion of a task/job can be done optimally

Mutex
Semaphore
Completion
None of the above

Answers : Answers to Linux Quiz on semaphores