Variables In Bash 
key=var
echo $key
var

Variables aren’t assigned until the shell encounters them.

Naming Rules #

  1. Variable names may consist of [:alnum:_]+
  2. The first character of a variable name must be either a letter or _
  3. Spaces and punctuation not allowed
  4. Common convention is for CONSTANTS to be uppercase and variables lowercase.

Assigning Values #

  • Treats all variables as strings.
  • No spaces in assignment. key= "var" won’t work, for example.
  • Can have multiple assignments on a single line: a=5 b="a string"

Expansion #

Variable names may be surrounded by optional curly braces, {} Useful when variable names become ambiguous.

[me@linuxbox ~]$ filename="myfile"
[me@linuxbox ~]$ touch "$filename"
[me@linuxbox ~]$ mv "$filename" "$filename1"
mv: missing destination file operand after `myfile'
Try `mv --help' for more information.
[me@linuxbox ~]$ mv "$filename" "${filename}1"

Good practice to enclose variables and command substitutions in double quotes to limit the effects of word-splitting by the shell.