Bash "local" Command (with examples)
The “local” command is a built-in command in Bash that is used to declare local variables and assign values to them. Local variables are variables that are only accessible within the scope of a function or script where they are defined.
In this article, we will explore different use cases of the “local” command and provide code examples for each use case. We will cover declaring string variables, integer variables, array variables, associative array variables, and readonly variables.
1: Declare a string variable with the specified value
local variable="value"
Motivation:
Declaring string variables with the “local” command allows us to store and manipulate textual data within our Bash scripts. By assigning a value to a string variable, we can easily refer to that value throughout our script without having to type it multiple times.
Explanation:
In this example, we use the “local” command to declare a string variable named “variable” and assign the value “value” to it. The syntax for declaring a string variable is local variable="value", where “variable” is the name of the variable and “value” is the desired value.
Example Output:
No output is produced by this command. It simply declares and assigns a value to the “variable” string variable.
2: Declare an integer variable with the specified value
local -i variable="value"
Motivation:
Declaring integer variables with the “local” command allows us to perform arithmetic operations and comparisons on numerical data within our Bash scripts. By declaring a variable as an integer, we ensure that it is treated as such, avoiding any unexpected behavior.
Explanation:
In this example, we use the “local” command with the -i option to declare an integer variable named “variable” and assign the value “value” to it. The syntax for declaring an integer variable is local -i variable="value". The value assigned to an integer variable can be a numerical value or an arithmetic expression.
Example Output:
No output is produced by this command. It simply declares and assigns a value to the “variable” integer variable.
3: Declare an array variable with the specified value
local variable=(item_a item_b item_c)
Motivation:
Declaring array variables with the “local” command allows us to store multiple values within a single variable. This can be useful when working with lists of items or when we need to group related data together.
Explanation:
In this example, we use the “local” command to declare an array variable named “variable” and assign the values “item_a”, “item_b”, and “item_c” to it. The syntax for declaring an array variable is local variable=(item_a item_b item_c), where “variable” is the name of the variable and “item_a”, “item_b”, and “item_c” are the desired values.
Example Output:
No output is produced by this command. It simply declares and assigns values to the “variable” array variable.
4: Declare an associative array variable with the specified value
local -A variable=([key_a]=item_a [key_b]=item_b [key_c]=item_c)
Motivation:
Declaring associative array variables with the “local” command allows us to store key-value pairs within a single variable. This can be useful when we want to associate values with specific keys, such as when working with configuration settings or lookup tables.
Explanation:
In this example, we use the “local” command with the -A option to declare an associative array variable named “variable” and assign the key-value pairs “key_a=item_a”, “key_b=item_b”, and “key_c=item_c” to it. The syntax for declaring an associative array variable is local -A variable=([key_a]=item_a [key_b]=item_b [key_c]=item_c), where “variable” is the name of the variable, “key_a”, “key_b”, and “key_c” are the keys, and “item_a”, “item_b”, and “item_c” are the corresponding values.
Example Output:
No output is produced by this command. It simply declares and assigns key-value pairs to the “variable” associative array variable.
5: Declare a readonly variable with the specified value
local -r variable="value"
Motivation:
Declaring readonly variables with the “local” command allows us to create constants within our Bash scripts. Once a variable is declared as readonly, its value cannot be changed or reassigned throughout the script, preventing accidental modifications.
Explanation:
In this example, we use the “local” command with the -r option to declare a readonly variable named “variable” and assign the value “value” to it. The syntax for declaring a readonly variable is local -r variable="value", where “variable” is the name of the variable and “value” is the desired value. Once a readonly variable is declared, any attempt to modify its value will result in an error.
Example Output:
No output is produced by this command. It simply declares and assigns a value to the “variable” readonly variable.
In conclusion, the “local” command in Bash is a powerful tool for declaring and assigning values to local variables. It allows us to store different types of data, such as strings, integers, arrays, and associative arrays, as well as create constants using readonly variables. By understanding the various use cases of the “local” command and its options, we can effectively manage and manipulate data within our Bash scripts.
