Adds bash tips

bash.md

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+# BASH
+
+## FLV to AVI conversion :
+
+You will need ffmpeg
+
+```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
+ ```
+
+## OGG to AVI conversion :
+
+You will need mencoder
+
+```bash
+$ sudo apt-get install mencoder
+$ mencoder out.ogv -ovc xvid -oac mp3lame -xvidencopts pass=1 -o Winner.avi
+```
+
+## Get the size of a file :
+
+Here are two simple ways:
+
+```bash
+$ ls -s file
+$ stat file-c %s
+```
+
+##Get the processing time of a function/script:
+
+Simply run the same command prepended with time
+
+```bash
+$ time previous_command
+```
+
+## Get the number of arguments in command line:
+
+Use the variable **$#** to get the number of arguments of previous command.
+
+__**WARNING:** The name of the command stands for one argument!__
+
+## Get the list of dependencies of a binary:
+
+Simply run the same command prepended with ldd :
+
+```bash
+$ ldd previous_command
+```
+
+## Demonize a process :
+
+The command to search for is **start-stop-daemon**, with start option.
+
+To avoid any output in stdout, use redirection:
+
+```bash
+$ command &> /dev/null&
+```
+
+## Launch a process at startup:
+
+A link must be placed in /etc/init.d, using ln -s
+
+```bash
+$ mv /etc/init.d
+$ ln -s /path/to/file link
+```
+
+__**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
+
+```bash
+trap " 2 3
+```
+
+where you want to ‘trap’ the command.
+
+End catching interruptions by adding where you want to stop
+
+```bash
+trap 2 3
+```
+
+## Use floats in a script, and convert them back to integers:
+
+The operations can be performed with bc :
+
+```bash
+$ VAR=$(echo "2.2/ 10.65" | bc -l)
+```
+
+To switch back to the int value :
+
+```bash
+$ (ceil) INT=${VAR/.*}
+```
+
+## Search for pattern in all files of a folder:
+
+```bash
+$ "find ./ -name .svn -prune -o -type f -print | xargs grep -Hi" //pattern//
+```
+
+The .svn part is used to avoid searching in the subversion folder of my projects.
+
+```bash
+$ grep -R //pattern//@@ is also a solution.
+```
+
+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:
+
+```bash
+$ vim ~/.bash_aliases
+```
+
+Simply add a new line at the end of the file :
+
+```bash
+alias_name = "my_one_line_command"
+```
+
+Restart your terminal, you’re done!
+
+## Seconds since epoch:
+
+```bash
+$ date -d "$FIRST_TIME" +"%s"
+```
+
+## Directly get the correct shebang for you script:
+
+```bash
+$ which //language// > my_script
+```
+
+Example :
+
+```bash
+$ which bash > my_script.sh
+```
+
+## Get the encoding of a file:
+
+```bash
+$ file -i //unkown_file_type//
+```
+
+## Remove all .svn folders from a repo:
+
+```bash
+$ cd //my_folder///
+$ find -name ".svn" -exec rm -rf {} \;
+```
+
+__**INFO:** Can be performed for any folder type, changing the .svn part__
+
+## Get information about your Linux version:
+
+Description file:
+```bash
+$ cat /etc/lsb-release
+```
+
+Kernel version:
+```bash
+$ uname -a
+```
+
+More information about Kernel (compiler and so on):
+```bash
+$ cat /proc/version
+```
+
+Get information about your processor(s):
+
+```bash
+$ cat /proc/cpuinfo
+```
+
+## Change default browser in Linux:
+
+```bash
+$ update-alternatives &&config x-www-browser
+```
+
+You will have to choose between all installed browsers in you distro.
+
+## Add a user to the sudoers:
+
+```bash
+$ visudo
+```
+
+Search for the line
+
+```bash
+@@ root ALL=(ALL) ALL@@
+```
+
+Add this new line just below :
+
+```bash
+user_name ALL=(ALL) ALL
+```
+
+## Get information about you graphical card:
+
+```bash
+$ lspci | grep VGA
+```
+
+You may try this if first is not working :
+
+```bash
+$ lspci | grep video
+```
+
+## Add tab completion for sudo commands:
+
+Add
+
+```bash
+complete -cf sudo
+```
+
+in your .bashrc. It can be done simply in running the following command once:
+
+```bash
+$ echo "complete -cf sudo" > ~/.bashrc
+```
+
+## Read information in elf files:
+
+```bash
+$ readelf -h $1 | grep 'Class\|File\|Machine'
+```
+
+## Sniff on serial interface to read output of a device :
+
+```bash
+$ sudo apt-get install jpnevulator
+$ jpnevulator --read --ascii --tty /dev/ttyUSB0
+```
+
+## Remove trailing / in path in a script:
+
+```bash
+#!/bin/bash
+FOLDER=$1
+echo ${FOLDER%/}
+```