useful bash commands

bash.sh

//download a whole youtube playlist as mp3 files:
youtube-dl -ix -k --audio-format mp3  YOUTUBE_PLAYLIST_URL

GREP
simple use of grep: 
grep -n search_string files //ej: grep -n main *.cpp
//list files that contains some string (only .c and .h in this example) -w forces exact word match.
grep --include=\*.{c,h} -rnw './' -e "your_search_string"

#concatenate two mp3 files.
mp3wrap destination.mp3 sources.mp3 
#example: source1.mp3 and source2.mp3 into destination mp3: mp3wrap destination.mp3 source*.mp3

 install fonts
sudo apt-get install fonts-cmu
sudo apt-get install --reinstall ttf-mscorefonts-installer

delete the lines of a text file from the given line number:
sed -i '300000,$d' LearnogramSpark15m.log

encode and decode binary files as base64
 uuencode -m hola.txt  hola.base64  > hola.base64
uudecode -o hola2.txt hola.base64

ENVIRONMENT VARS:
printenv                   #print all the global env.vars (just "set" prints both global and local)
echo $var_name             #print a var by name
export var_name=value      #export a var globally. just assign to create a local var (no export)
unset var_name             #remove the var
~/.bash_profile            #edit this file to persist changes for the given user
/etc/environment           #edit this file to persist changes for all the users
how to add to .bashrc: 
export PATH=$PATH:NEW_PATH