#Check if a program exists
command -v foo >/dev/null 2>&1 || { echo >&2 "I require foo but it's not installed.  Aborting."; exit 1; }

#Block Comment in bash
: '
This is a test comment
Author foo bar
Released under GNU
'

#Unicode escape in bash
<var_name>=$'\xe2\x98\xa2 '

# if-else
if [ "foo" = "foo" ]; then
   echo expression evaluated as true
else
   echo expression evaluated as false
fi

# Grep only Numeric values:
echo "99%" |grep -o '[0-9]*'

# Bash Command output to a variable
OUTPUT="$(ls -1)"
echo "${OUTPUT}"

# SED w variable and line replace
sed -i.bak 's/.*TEXT_TO_BE_REPLACED.*/"'$VARIABLE'"/' VagrantFile >/dev/null 2>&1

# While loop
i="0"
while [ $i -lt 4 ]
do
i=$[$i+1]
done

# Redirect Command output
command 2> /dev/null

#Detect OS
platform='unknown'
unamestr=`uname`
if [[ "$unamestr" == 'Linux' ]]; then
   platform='linux'
elif [[ "$unamestr" == 'FreeBSD' ]]; then
   platform='freebsd'
fi

# Execute a Gist in bash
#http://max.disposia.org/notes/bash-exec-gist.htm
bash -c "$(curl -fsSL $raw_gist_path)" $arg0 $arg1

# Append multiple lines to a file
cat <<EOT >> greetings.txt
line 1
line 2
EOT

# Change Password using script
echo "USERNAME:NEWPASSWORD" | chpasswd

# Generate SSH key using script
echo -e "\n\n\n" | ssh-keygen -t rsa

# SSH Key using script
sudo apt-get install sshpass
sshpass -p "PASSWORD" ssh-copy-id -o StrictHostKeyChecking=no USERNAME@IP

# Process spawn and wait
/my/process &
/another/process &
wait
echo "All processes done!"

# Alert in bash
echo -e "\a"

# Create offline Installation
sudo apt-get download PACKAGE_NAME && apt-cache depends -i PACKAGE_NAME | awk '/Depends:/ {print $2}' | xargs  apt-get download

# Arrays in Bash
ARRAY=(one two three)
echo ${ARRAY[*]} # Print all
echo ${ARRAY[2]} # Print 3rd element

# For loop
for VARIABLE in 1 2 3 4 5 .. N
do
	command1
	command2
	commandN
done

# Iterating through each directory
for f in *; do
    if [ -d ${f} ]; then
        # Will not run if no directories are available
        echo $f
    fi
done

# Iterating through an array with index
for i in "${!foo[@]}"; do 
  printf "%s\t%s\n" "$i" "${foo[$i]}"
done

# Single line condition checker
if ps aux | grep some_proces[s] > /tmp/test.txt; then echo 1; else echo 0; fi

# Array Declaration
array=(1 2 3)
# Print 1st Element
echo ${array[1]}
# Print all elements
echo ${array[@]}
# Get length of an array
echo ${#VAR_NAME[@]}

#Split Name 
IN="bla@some.com;john@home.com"
arrIN=(${IN//;/ })

# Silent execution
silent() {
    "$@" > /dev/null 2>&1
}
silent echo "Hello World"

#Switch Case
case "$C" in
"1")
    do_this()
    ;;
"2" | "3")
    do_what_you_are_supposed_to_do()
    ;;
*)
    do_nothing()
    ;;
esac

# Adding multiple lines to a file
cat <<EOT >> FILENAME
export KUBE_VERSION=1.2.0
export FLANNEL_VERSION=0.5.0
export ETCD_VERSION=2.2.0
export nodes="vagrant@10.0.168.10 vagrant@10.0.168.11 vagrant@10.0.168.11"
export roles="ai i i"
export NUM_NODES=${NUM_NODES:-3}
export SERVICE_CLUSTER_IP_RANGE=192.168.3.0/24
export FLANNEL_NET=172.16.0.0/16
EOT

# Grep select only numbers
echo "99%" |grep -o '[0-9]*'

# Create a sample from files in a folder
mkdir -p sample
for f in *.csv; do head -101 $f >> sample/$f; done

# Kill app based on port number
PID=`lsof -i:8121 -t`
echo "Stopping previous build if any . . ." && kill -9 ${PID}

# Set Locale
export LC_ALL=en_US.UTF-8  
export LANG=en_US.UTF-8

# Convert multiline bash output to an array
var=($(./inner.sh))

# Grep IP Address using regex
echo "$str_containing_ip_addrs" | grep -oE "\b([0-9]{1,3}\.){3}[0-9]{1,3}\b"

# Wait for previous process while executing another command
launch backgroundprocess &
PROC_ID=$!

while kill -0 "$PROC_ID" >/dev/null 2>&1; do
    echo "PROCESS IS RUNNING"
done
echo "PROCESS TERMINATED"
exit 0

# To log every command before execution
set -o xtrace # to revert to normal - set +o xtrace
# or bash -x myscript.sh

#list process on port
lsof -i tcp:<port number> 

#Select random lines from a file
shuf -n N input > output

# Generate a random number between 1-10
$(( ( RANDOM % 10 )  + 1 ))