Question

In Windows, how do you access arguments passed when a batch file is run?

For example, let’s say I have a program named hello.bat. When I enter hello -a at a Windows command line, how do I let my program know that -a was passed in as an argument?

Answer 1

As others have already said, parameters passed through the command line can be accessed in batch files with the notation %1 to %9. There are also two other tokens that you can use:

• %0 is the executable (batch file) name as specified in the command line.
• %* is all parameters specified in the command line — this is very useful if you want to forward the parameters to another program.

There are also lots of important techniques to be aware of in addition to simply how to access the parameters.

Checking if a parameter was passed

This is done with constructs like IF "%~1"=="", which is true if and only if no arguments were passed at all. Note the tilde character which causes any surrounding quotes to be removed from the value of %1; without a tilde you will get unexpected results if that value includes double quotes, including the possibility of syntax errors.

Handling more than 9 arguments (or just making life easier)

If you need to access more than 9 arguments you have to use the command SHIFT. This command shifts the values of all arguments one place, so that %0 takes the value of %1, %1 takes the value of %2, etc. %9 takes the value of the tenth argument (if one is present), which was not available through any variable before calling SHIFT (enter command SHIFT /? for more options).

SHIFT is also useful when you want to easily process parameters without requiring that they are presented in a specific order. For example, a script may recognize the flags -a and -b in any order. A good way to parse the command line in such cases is

:parse
IF "%~1"=="" GOTO endparse
IF "%~1"=="-a" REM do something
IF "%~1"=="-b" REM do something else
SHIFT
GOTO parse
:endparse
REM ready for action!

This scheme allows you to parse pretty complex command lines without going insane.

Substitution of batch parameters

For parameters that represent file names the shell provides lots of functionality related to working with files that is not accessible in any other way. This functionality is accessed with constructs that begin with %~.

For example, to get the size of the file passed in as an argument use

ECHO %~z1

To get the path of the directory where the batch file was launched from (very useful!) you can use

ECHO %~dp0

You can view the full range of these capabilities by typing CALL /? in the command prompt.