variables in shell scripting

variables in shell scripting:

Shell variables are created once they are assigned a value. A variable can contain a number, a character or a string of characters. Variable name is case sensitive and can consist of a combination of letters and the underscore "_". Value assignment is done using the "=" sign. Note that no space permitted on either side of = sign when initializing variables.

EX:

PRICE_PER_APPLE=5
MyFirstLetters=ABC
greeting='Hello        world!'

1. A backslash "\" is used to escape special character meaning

EX:

PRICE_PER_APPLE=5
echo "The price of an Apple today is: \$HK $PRICE_PER_APPLE"
o/p: The price of an Apple today is: $HK 5 
  

2. Encapsulating the variable name with ${} is used to avoid ambiguity

EX:

MyFirstLetters=ABC
echo "The first 10 letters in the alphabet are: ${MyFirstLetters}DEFGHIJ"
o/p: The first 10 letters in the alphabet are: ABCDEFGHIJ
 
3. Encapsulating the variable name with "" will preserve any white space values 
  

EX:

greeting='Hello        world!'
echo $greeting" now with spaces: $greeting"
o/p:Hello world! now with spaces: Hello        world!
 
4. Variables can be assigned with the value of a 
command output. This is referred to as substitution. Substitution can be
done by encapsulating the command with `` (known as back-ticks) or with $() 
 
EX:
FILELIST=`ls`
FileWithTimeStamp=/tmp/my-dir/file_$(/bin/date +%Y-%m-%d).txt