Comment-Remark - CMD

Overview

The :: is a feature in Windows Command Prompt (CMD) used as a way to introduce comments in batch scripts. Unlike the more commonly known REM command, :: is treated as a label, making it effectively ignored by the command processor. It is primarily used for adding explanatory text or temporarily disabling parts of a script. It is most effectively used in scripting scenarios to improve readability and script maintenance.

Syntax

The syntax for using the :: command is straightforward:

:: [comment text]
  • [comment text]: This can be any text that explains or comments on a section of the batch file.

Since :: is treated as a label, no actual command execution takes place, and no arguments or options are strictly applicable to it, besides the comment itself.

Options/Flags

As a comment syntax, :: does not have options or flags. Its sole purpose is to provide a comment within scripts.

Examples

  • Simple Commenting

    :: This is a simple comment
ECHO Hello, World!

  • Commenting Out Code

    :: ECHO This line will not execute
ECHO This line will execute

  • Using alongside actual code

    ECHO Start of the script
:: Initialize variables
SET var=Example
ECHO %var%

Common Issues

  • Using :: inside code blocks: If used inside a command block (surrounded by parentheses), it might cause unexpected behavior or errors. Use REM instead in these scenarios.

    (
    ECHO Before comment
    :: This might cause an error
    ECHO After comment
)

  • Visibility in command output: Unlike REM, which can display in the script’s output when ECHO is on, :: remains invisible but might occasionally clutter the output if incorrectly parsed.

Integration

:: can be used alongside any CMD command to explain steps or disable code during debugging. Here’s how it integrates into a more complex script:

:: Check disk space before installation
IF EXIST C:\install.log (
    :: Log file exists, check size
    FOR %%V IN (C:\install.log) DO SET size=%%~zV
    IF %size% GTR 1024 ECHO Log file too large
)

  • REM: Officially supported way to insert comments. Good to use in complex scripts especially within conditional or loop blocks.

  • ECHO: Used to print text to the screen, can be used to output comments if needed for debugging purposes.

For detailed usage of batch scripting and command syntax, consider referring to the official Microsoft documentation or resources like SS64.com.