The export command in various operating systems allows you to set environment variables or make them available to child processes. The specifics of the export command can vary slightly depending on the operating system you are using. Here's an explanation of how the export command works in different environments:

1. Unix/Linux:
   • In Unix and Linux systems, the export command is used to set environment variables that are accessible to the current shell session and any child processes spawned from it.
   • Syntax: export VARIABLE_NAME=VALUE
   • Example: export PATH=/usr/local/bin:$PATH
     • This example sets the PATH environment variable to include /usr/local/bin and appends the existing PATH value to it.
   • The changes made using export are effective only within the current shell session and its child processes. They are not persistent across different sessions or system reboots.
2. Windows:
   • In Windows, the export command is not used. Instead, the equivalent command is set, which sets environment variables within the current shell session.
   • Syntax: set VARIABLE_NAME=VALUE
   • Example: set PATH=C:\\\\Program Files\\\\Java\\\\jdk1.8.0_201\\\\bin;%PATH%
     • This example sets the PATH environment variable to include C:\\\\Program Files\\\\Java\\\\jdk1.8.0_201\\\\bin and appends the existing PATH value to it using the %PATH% placeholder.
   • Similar to Unix/Linux, the changes made using set in Windows are effective only within the current shell session and its child processes. They are not persistent across different sessions or system reboots.
3. Exporting Variables for Scripts:

   • In both Unix/Linux and Windows, when running scripts, you can use the export or set command within the script itself to set environment variables for that specific script execution.

   • Example (Unix/Linux):

     #!/bin/bash
     export MY_VARIABLE="Hello, World!"
     echo $MY_VARIABLE
     
     

   • Example (Windows batch script):

     @echo off
     set MY_VARIABLE=Hello, World!
     echo %MY_VARIABLE%
     
     

Remember that environment variables set using export or set are specific to the current session and its child processes. To make the changes persistent or affect the entire system, you may need to modify system configuration files or use other mechanisms provided by the respective operating systems.

It's important to note that the export command may have different behaviors and usage in specific shells or scripting languages. Always refer to the documentation or man pages of your specific environment for accurate and detailed information.