Defining Variables in Bash Scripts: With or Without Export

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In Bash scripting, defining variables can be straightforward, but understanding when to use export can affect how variables are accessed and manipulated within scripts and across processes. This guide clarifies the usage of defining variables with and without export in Bash scripts.

Understanding Variable Definition

In Bash, variables are typically defined using the syntax variable_name=value. This assignment sets the value of variable_name to value within the current shell session.

Example:

#!/bin/bash

my_var="Hello, World!"
echo $my_var

In this example, my_var is defined and assigned the value "Hello, World!". The echo command then prints the value of my_var.

Using export with Variables

The export command makes variables available to child processes of the current shell. This is particularly useful when you need environment variables to be inherited by processes launched from your script.

Example:

#!/bin/bash

export MY_ENV_VAR="Important Data"
./child_script.sh

In this example:

  • MY_ENV_VAR is defined and exported with the value "Important Data".
  • ./child_script.sh is a child script that can access MY_ENV_VAR as an environment variable.

Differences Between Exported and Non-Exported Variables

  1. Visibility: Exported variables are visible to child processes, while non-exported variables are only accessible within the current shell session.
  2. Environment Variables: Exported variables become environment variables, which can be useful for configuring programs or scripts that depend on specific settings.

When to Use export

Use export when:

  • You need a variable to be available to processes launched from your script.
  • You want to set environment variables that affect program behavior or configuration.

When Not to Use export

Avoid using export when:

  • Variables are only needed within the current shell session and its child processes.
  • Variables contain data that does not need to be shared globally among all processes.

Conclusion

Understanding how to define variables with and without export in Bash scripts is crucial for managing script behavior, environment configuration, and inter-process communication. By using export, you ensure variables are accessible as environment variables across processes, while non-exported variables remain local to the current shell session.

With this knowledge, you can effectively manage variable scope and accessibility in Bash scripting, optimizing script behavior and facilitating robust application configurations.