Tohuwabohu excorcism

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Shell or Bash Scripts

Shebang	Header, which tells where the interpreter is located #!/bin/sh	http://stackoverflow.com/questions/10376206/what-is-the-preferred-bash-shebang
Sourcing	launch script in a new shell using point with an empty space between sript path Souring: . path/to/script.sh vs Execute in current shell: ./path/to/script.sh	http://superuser.com/questions/176783/what-is-the-difference-between-executing-a-bash-script-and-sourcing-a-bash-scrip

Guides

http://www.artificialworlds.net/blog/2012/10/17/bash-associative-array-examples/

https://linuxconfig.org/bash-scripting-tutorial

http://www.tldp.org/LDP/Bash-Beginners-Guide/html/Bash-Beginners-Guide.html#chap_11

http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html

Executing or Sourcing the script

Sourcing. Execute in the CURRENT shell

. path/to/script.sh

Executing. Execute in a NEW shell - e.g. cd doesn't modify current path

./path/to/script.sh

declare Function

Returning result is done via echo

#!/bin/bash

#Define bash global variable
#This variable is global and can be used anywhere in this bash script
VAR="global variable"

function bash {
  #Define bash local variable
  #This variable is local to bash function only
  local VAR="local variable"
  echo $VAR
}
echo $VAR
bash

# Note the bash global variable did not change
# "local" is bash reserved word
echo $VAR

declare Array

Small a!!!

	declare -a map

	map[1]="myvalue"
	map[1]="myvalue2"

	echo ${map[1]}

declare Map

Big A!!!

	declare -A map

	map[test]="myvalue"
	map[test2]="myvalue2"

	echo ${map[test2]}

iterate array keys

Access via ${!array[@]}

for i in "${!array[@]}"
do
  echo "key  : $i"
  echo "value: ${array[$i]}"
done

dereference an array / map value

${ARRAY[2]}
${map[key1]}

If Else

Empty spaces after the parenthesis are critical: [ $a==$b ]

# check if it is the root device
if [ $device_name==$root_device_name ]
then
	echo "$device_name is root"
else
	echo "NOT root"
fi

Command Substitution

Command substitution allows the output of a command to replace the command itself. Command substitution occurs when a command is enclosed like this:

$(command)

or like this using backticks:

`command`

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