jlengrand/jlengrand.github.io

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Julien Lengrand-Lambert e11060535f Replacing all links with HTTPS

2018-03-17 11:04:40 +01:00

23 KiB

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BASH

FLV to AVI conversion :

You will need ffmpeg

{% highlight bash %} $ sudo apt-get install ffmpeg $ ffmpeg -o /your/flv/file.flv -vcodec mpeg1-video
-acodec copy -ar 44100 -s 320x240 -y /your/avi/file.avi {% endhighlight %}

OGG to AVI conversion :

You will need mencoder

{% highlight bash %} $ sudo apt-get install mencoder $ mencoder out.ogv -ovc xvid -oac mp3lame -xvidencopts pass=1 -o Winner.avi {% endhighlight %}

Get the size of a file :

Here are two simple ways:

{% highlight bash %} $ ls -s file $ stat file-c %s {% endhighlight %}

Get the processing time of a function/script:

Simply run the same command prepended with time

{% highlight bash %} $ time previous_command {% endhighlight %}

Get the number of arguments in command line:

Use the variable $# to get the number of arguments of previous command.

WARNING: The name of the command stands for one argument!

Get the list of dependencies of a binary:

Simply run the same command prepended with ldd :

{% highlight bash %} $ ldd previous_command {% endhighlight %}

Demonize a process :

The command to search for is start-stop-daemon, with start option.

To avoid any output in stdout, use redirection:

{% highlight bash %} $ command &> /dev/null& {% endhighlight %}

Launch a process at startup:

A link must be placed in /etc/init.d, using ln -s

{% highlight bash %}

$ mv /etc/init.d

$ ln -s /path/to/file link

{% endhighlight %}

WARNING: A printf in a startup process will lead to a crash as it blocks the remaining processes.

INFO: In embedded Linux, startup processes will have to be named using a Sxx name, where xx is a digit between 1 and 99.

The processes will be run in ascending order, so be careful not to block the system (samba after network, . . . )

Block interruptions (CTRL+C) :

Simply add the line

{% highlight bash %}

trap " 2 3

{% endhighlight %}

where you want to 'trap' the command.

End catching interruptions by adding where you want to stop

{% highlight bash %}

trap 2 3

{% endhighlight %}

Use floats in a script, and convert them back to integers:

The operations can be performed with bc :

{% highlight bash %}

$ VAR=$(echo "2.2/ 10.65" | bc -l)

{% endhighlight %}

To switch back to the int value :

{% highlight bash %}

$ (ceil) INT=${VAR/.*}

{% endhighlight %}

Search for pattern in all files of a folder:

{% highlight bash %}

$ "find ./ -name .svn -prune -o -type f -print | xargs grep -Hi" //pattern//

{% endhighlight %}

The .svn part is used to avoid searching in the subversion folder of my projects.

{% highlight bash %}

$ grep -R //pattern//@@ is also a solution.

{% endhighlight %}

It is even possible to create an alias with it (see Add a one line command in terminal).

Add a one line command in terminal:

You may use some one-line commands lots of times a day in terminal.

You can define aliases to gain productivity:

{% highlight bash %}

$ vim ~/.bash_aliases

{% endhighlight %}

Simply add a new line at the end of the file :

{% highlight bash %}

alias_name = "my_one_line_command"

{% endhighlight %}

Restart your terminal, you're done!

Seconds since epoch:

{% highlight bash %}

$ date -d "$FIRST_TIME" +"%s"

{% endhighlight %}

Directly get the correct shebang for you script:

{% highlight bash %}

$ which //language// > my_script

{% endhighlight %}

Example :

{% highlight bash %}

$ which bash > my_script.sh

{% endhighlight %}

Get the encoding of a file:

{% highlight bash %}

$ file -i //unkown_file_type//

{% endhighlight %}

Remove all .svn folders from a repo:

{% highlight bash %}

$ cd //my_folder///

$ find -name ".svn" -exec rm -rf {} ;

{% endhighlight %}

INFO: Can be performed for any folder type, changing the .svn part

Get information about your Linux version:

Description file:

{% highlight bash %}

$ cat /etc/lsb-release

{% endhighlight %}

Kernel version:

{% highlight bash %}

$ uname -a

{% endhighlight %}

More information about Kernel (compiler and so on):

{% highlight bash %}

$ cat /proc/version

{% endhighlight %}

Get information about your processor(s):

{% highlight bash %}

$ cat /proc/cpuinfo

{% endhighlight %}

Change default browser in Linux:

{% highlight bash %}

$ update-alternatives &&config x-www-browser

{% endhighlight %}

You will have to choose between all installed browsers in you distro.

Add a user to the sudoers:

{% highlight bash %}

$ visudo

{% endhighlight %}

Search for the line

{% highlight bash %}

@@ root ALL=(ALL) ALL@@

{% endhighlight %}

Add this new line just below :

{% highlight bash %}

user_name ALL=(ALL) ALL

{% endhighlight %}

Get information about you graphical card:

{% highlight bash %}

$ lspci | grep VGA

{% endhighlight %}

You may try this if first is not working :

{% highlight bash %}

$ lspci | grep video

{% endhighlight %}

Add tab completion for sudo commands:

Add

{% highlight bash %}

complete -cf sudo

{% endhighlight %}

in your .bashrc. It can be done simply in running the following command once:

{% highlight bash %}

$ echo "complete -cf sudo" > ~/.bashrc

{% endhighlight %}

Read information in elf files:

{% highlight bash %}

$ readelf -h $1 | grep 'Class|File|Machine'

{% endhighlight %}

Sniff on serial interface to read output of a device :

{% highlight bash %}

$ sudo apt-get install jpnevulator

$ jpnevulator --read --ascii --tty /dev/ttyUSB0

{% endhighlight %}

Remove trailing / in path in a script:

{% highlight bash %}

#!/bin/bash

FOLDER=$1

echo ${FOLDER%/}

{% endhighlight %}

PYTHON

Get variable name as a string:

{% highlight python %}

blah = 1

blah_name = [ k for k , v in locals (). iteritems () if v is blah ][ 0 ]

{% endhighlight %}

WARNING : Not very clever however, as variables in Python may have more that one name ! Use with caution!

Replace a part of a table [Numpy]:

{% highlight python %}

small_BW=where((L[temp[ptr-1]]==ptr),1,0)

a=BW[posi_0:posi_1,posi_2:posi_3]

a[:,:]=small_BW.copy()

{% endhighlight %}

Reshape table without size information:

Put -1 as second argument, the info will automatically be processed.

{% highlight python %}

array.reshape(3,-1)

{% endhighlight %}

Concatenate 2 tables [Numpy]:

{% highlight python %}

c=numpy.concatenate((a,b),axis=0)

{% endhighlight %}

Cast data in table to int:

{% highlight python %}

Ndarray.astype(int)

{% endhighlight %}

Write in the end of a file :

Use add mode :

{% highlight python %}

file.open(file_name, 'a')

{% endhighlight %}

Test if variable exists:

{% highlight python %} try: print variable except NameError: print "Error!" {% endhighlight %}

Check if variable is one of several choices:

{% highlight python %} if a in [b, c,d]: blabla {% endhighlight %}

Multi instanciation in Python:

{% highlight python %} a = b = c = 1+1 {% endhighlight %}

WARNING: Those three variables are the same object!

Print function name :

{% highlight python %} import sys

def tutut(): """ Dum function displaying its name! """ print sys._getframe().f_code.co_name

if name == 'main': tutut() {% endhighlight %}

And here is the result

{% highlight bash %} [airballman@ubuntu:~]$ python tutut.py tutut {% endhighlight %}

C/C++

Block interruptions (CTRL+C):

Include the signal header :

[c] #include signal.h [/c]

At the beginning of the main, insert

[c] signal(SIGINT, fction) [/c]

with

fction the function to be started on detection.
SIGINT the interrupt to be detected.

Some simple basics that helped :

About variables :

age -> value
&age -> pointer

About pointers :

ptr -> ptr value(which is an address)
*ptr -> variable value placed in the address.

If age is a variable :

age is its value
&age is its pointer

If ptr is a pointer :

ptr is the pointer value (which is an address)
*ptr is the value of the variable contained in at the address.

Pointers creation:

[c] int *ptr = NULL; //Is just a creation, the * does not stand for anything else than declaring the pointer.

int age = 10;

*ptr=&age; //ptr is already created, the * now means that whe want to assign its value [/c]

Those two are equivalent (used for structures):

a->b
*(a.b)

Define a variable in a Makefile :

Use the -D option in the CFLAGS
#define in the C code

Git and GitHub

Simple reminders to manage a project with Git and GitHub interface.

Clone a project from my personal GitHub account:

{% highlight bash %} $ git clone git@github.com:jlengrand&/projet.git {% endhighlight %}

Clone a project from another source:

{% highlight bash %} $ git clone git://git.berlios.de/gpsd {% endhighlight %}

Push modifications previously locally committed:

Should be performed once in a while to keep remote repository up to date. Do not forget to pull before pushing to avoid conflicts.

{% highlight bash %} $ git push -origin master {% endhighlight %}

More information can be found in git documentation

INFO : No need to create a folder first, as a main folder is automatically created for the project.

Electronics

Some basic tipe for new embedded Eletronics programmers (like me ;) )

Use of DDx, PORT and PIN registers:

DDx: Choice of pins state: Inputs or Outputs
PORT: Set the outputs state, rules the outputs (ex : set Pin to 0)
PIN: Reads the inputs states, or toggle values. (ex: Toogle Pin)

Easily set a bit to 0 in a register:

[c] PPR=PPR & 0b01111111 [/c]

Easily set a bit to 1 in a register:

[c] PPR=PPR & 0b01111111 [/c]

Debug hardware errors after optimization:

In case your C code does not work any more after Optimization (-O2 -O3)

Check if global variables are used in interruptions
Try to set them as volatile

Hazardous hardware resets:

Check if your interruptions are initialized in your code !

Otherwise, the C code will automatically jump to a non-existing address, causing the reset.

I/O problems:

In case of I/O problems in your code, check your Hardware and especially your resistors

Try to unsolder them and run the code.

Embedded electronics main architecture code:

Generally, embedded architecture software is divided into 3 main layers :

Drivers: Whose job is to interact with Hardware at a low level (Ex : Read spi data)
Services/Components: Intermediate layer, interface between drivers and Applications
Application: Higher layer, which aims at achieving the main purpose of the project (Ex: Calculate movement using an accelerometer)

Here is a simple drawing to get the idea:

[caption id="" align="aligncenter" width="881" caption="Embedded Architecture Drawing"]

[/caption]

INFO: The main idea behind that when you code is the reuse! The application may not be reusable, but drivers and components must ! If you did good, you should be able to use the same application in two architectures, changing only components and drivers.

OpenCV

Memos and Tips about the OpenCV library.

In C/C++:

Place a pointer to the beginning of pixel in an image:

Can be used to naviguate through pixels easily (and more efficiently than some openCV functions).

[c] char *pImage = iplImage->ImageData [/c]

Short review of the IplImage structure:

What's really needed to work with an Image

[c]

IplImage struct { depth # Number of channels (gray level, color, . . .) sizeX sizeY
- ImageData } #Pixels of the image ...} [/c]

Simple tips for Image Processing optimization in C:

An image is stored in a memory a a long line (n*m size)

Always go trough the buffer way, and not the opposite!

[c] for (i in nb_lines): for (j in nb_cols): //do stuff } } [/c]

and

[c] for (j in nb_cols): for (i in nb_lines): //do stuff } } [/c]

are different !

The second one is 10% faster than the other !

In Python :

Error on compiling OpenCV with Python bindings:

If you get this error when trying to compile OpenCV in Linux

{% highlight bash %}

Could NOT find PythonLibs (missing: PYTHON_INCLUDE_DIRS) in cmake

{% endhighlight %}

Simply try installing python-dev packages.

It should solve the problem.

Subversion

To create a new branch in one of your repositories:

Copy your trunk folder. This will automatically proceed the mkdir

{% highlight bash %}

$ svn cp trunk -> new_branch

{% endhighlight %}

Update the information

{% highlight bash %}

$ svn update

{% endhighlight %}

INFO: The command is an update and not a commit, as this is the server who performed the operation!

You're done!

Merge your branch back in your trunk:

Move to your trunk folder

{% highlight bash %}

$ cd path/to/my/trunk

{% endhighlight %}

Merge the branch:

{% endhighlight %}

$ svn merge --reintegrate ./^branch

{% endhighlight %}

INFO: The reintegrate option allows continuing to work in the branch even once reintegrated

Some tips:

A tag is used to get a precise version, fixed in time (Ex : V1.1)
The trunk must always stay as the main reference to branches and tags (ie. cd /my/trunk before operations).
Always use the ^ sign to merge and branch folders. It allows to avoid using absolute path.

The ^ corresponds to /path/to/my/svn/root/folder
If you're running Windows, you might want to look at tortoisesvn.

Profiling

Simple tips for software profiling using Linux.

Simple steps on using gprof:

gprof is a really efficient prototyping tool designed by Richard Stallman

It is a total graal to exactly know where your bottlenecks are, and which parts of your software have to be optimized first!

Simply install gprof on your computer (for debian based distros).

{% highlight bash %}

$ sudo apt-get install gprof

{% endhighlight %}

Compile your C code with the -pg option
Execute your program, just as usual
You will see that a gmon.out file was created during the execution
You can retrieve the results of profiling by running gprof:

{% highlight bash %}

$ gprof your_binary gmon.out >> saved_report

$ vim saved_report

{% endhighlight %}

Simple command-line to search for memory leacks:

Using the Valgrind library.

{% highlight bash %}

$ valgrind --tool=memcheck --leak-check=yes --show-reachable=yes --num-callers=20 --track-fds=yes ./test

{% endhighlight %}

Wordpress

Some very simple tips and hints for wordpress.

Insert an horizontal line in a post :

Simply insert the

tag while in html edition mode .

Insert anchors/links in a section of a page:

This is done in two different steps :

Define the anchor. You should place the following code where you want the user to be redirected.

[html]your article here.[/html]

Create a link to the anchor. Depending on what you want, you should insert :

If the anchor is placed in the same page :

[html]my highlighted text[/html]

If the anchor is in another page :

[html]my highlighted text my highlighted text [/html]

You can see the result everywhere on this page, in the topic listing :).

23 KiB Raw Blame History

BASH

PYTHON

C/C++

Git and GitHub

Electronics

OpenCV

Subversion

Profiling

Wordpress

23 KiB

Raw Blame History