How do subshells differ from functions?

Subshells and functions in Bash serve different purposes and have distinct characteristics:

Subshells

• Definition: A subshell is a separate instance of the shell that is created when you enclose commands in parentheses ().
• Scope: Variables defined in a subshell are not accessible in the parent shell. Changes made to the environment in a subshell do not affect the parent shell.
• Usage: Subshells are often used for grouping commands, executing commands in a separate environment, or capturing output.

Example:

( 
  var="Hello from subshell"
  echo $var  # Outputs: Hello from subshell
)

echo $var  # Outputs nothing, as var is not accessible here

Functions

• Definition: A function is a block of reusable code defined using the function_name() { ... } syntax.
• Scope: Variables defined in a function can be accessed in the parent shell unless they are declared as local using the local keyword.
• Usage: Functions are used to encapsulate code for reuse, improve code organization, and make scripts more modular.

Example:

my_function() {
  local var="Hello from function"
  echo $var  # Outputs: Hello from function
}

my_function
echo $var  # Outputs nothing, as var is local to the function

Summary

• Subshells create a new shell environment and do not share variables with the parent shell.
• Functions are reusable code blocks that can share variables with the parent shell unless declared local.