Understanding the Differences: CALL vs. START /WAIT in Batch Scripting

Introduction

Batch scripting is a powerful way to automate tasks on Windows systems using command-line instructions stored in .bat files. Two commands often used within batch scripts for controlling program execution are CALL and START. This tutorial explores the differences between these two commands, specifically focusing on how they behave when executing applications such as executables or other batch files.

CALL Command

The CALL command is primarily used to invoke one batch file from another. It allows control to return to the calling script after the called script has finished executing. This makes it useful for scenarios where you need sequential execution of scripts while maintaining access to variables and environment settings across them.

Key Features:

• Sequential Execution: The calling batch script waits until the called batch file completes before resuming.
• Variable Context Sharing: Any changes made to environment variables or script labels within the called script are reflected back in the caller script.
• Simplicity with Executables: When invoking an executable, CALL behaves similarly to directly running the program. It executes synchronously without creating a new window.

Example:

@echo off
call another_script.bat
echo Script execution completed.

In this example, another_script.bat is executed, and control returns to the main script only after its completion.

START Command with /WAIT

The START command initiates a separate process for executing programs or scripts. When combined with the /WAIT option, it can synchronize execution by pausing the calling script until the specified program terminates.

Key Features:

• New Process Creation: Executes the target in a new instance of cmd.exe, which means it creates its own environment and variable context.
• Window Control Options: Allows additional parameters to control window behavior (minimized, maximized, hidden).
• Synchronization with /WAIT: The calling script pauses until the process associated with START completes.

Example:

@echo off
start /wait notepad.exe
echo Notepad has closed.

This example opens Notepad and waits for its closure before proceeding to echo a message.

Comparison Scenarios

1. Environment Variables:

   • With CALL, any changes in environment variables persist across scripts.
   • With START /WAIT, changes are confined to the new process, reverting once it finishes.

2. Parallel Execution:

   • CALL is ideal for running batch files sequentially while sharing context.
   • START /WAIT can be used for parallel execution of executables, ensuring synchronization upon completion.

3. Error Levels:

   • START /WAIT captures the exit codes from the executed program, useful in error handling scenarios.
   • CALL, when used with batch files, allows manipulation of labels and continuation based on script logic.

Best Practices

• Use CALL for tasks involving multiple scripts where shared context is necessary.
• Opt for START /WAIT when executing external applications that require synchronization or specific window management.
• Consider error handling capabilities: START /WAIT is beneficial to capture exit statuses of executables effectively.

By understanding these commands and their appropriate use cases, you can optimize your batch scripts for efficiency and reliability in automation tasks.