The difference between parameter and variable in bash

Last Updated on Friday, 01 April 2011 18:20

Question:

Hi, in bash context what is the difference between parameter and variable?

Answer:

In a bash context a parameter is an entity that stores values. Furthermore, a parameter can be a name ( variable ), number ( positional parameter ) or special character ( special parameter ). Therefore, a variable is a parameter denoted by a name. ( see: man bash ). Let's have a closer look on all three bash parameters:

1. Variable

Variable has a value assigned to it. It also can have 0 or more attributes. A value may be assigned to a variable by a following statement:

name=[value]

Example:

#!/bin/bash

myname="Gnu Bash"
printf "%s\n" "$myname"

2. Positional parameter

Positional parameter is denoted by one or digits. It is assigned by one or more arguments supplied to a script upon the script execution.
Example:

 #!/bin/bash

printf "%s\n" "My name is $1 $2"

3. Special Parameters

Special parameters are denoted by a one or more special characters from a following list: *, @, #, ?, -, $, !, 0 and _ . For example * expands to positional parameters. In other words it prints all arguments supplied on the command line upon the script execution:

 #!/bin/bash
echo $*

OUTPUT:

./special GNU Bash parameter vs variable
GNU Bash parameter vs variable

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