Windows batch files local variables

Viewed k times. I'm trying to define and use a variable in a batch file. Why is my variable not being echo'd? Magoo Jamie Dixon Jamie Dixon Add a comment. Active Oldest Votes. Brian Nixon Brian Nixon 8, 1 1 gold badge 16 16 silver badges 24 24 bronze badges. Is that a typo? So this is what MS came with — Falaque. Are there any downsides for the last syntax? Wolf - No, there is no downside. However, there is a limit to when it is most effective.

As long as the value does not contain quotes, then almost any characters can appear in the value without worrying about escaping. I also use this trick frequently to determine the name of the script at runtime.

The prefixing helps the end user by knowing the output is from the script and not another program being called by the script. It may sound silly until you spend hours trying to track down an obtuse error message generated by a script. Trust me, you want command processor extensions. I use this variable to make fully qualified filepaths to any other files in the same directory as our script.

Variable Declaration DOS does not require declaration of variables. Listing Existing Variables The SET command with no arguments will list all variables for the current command prompt session. Variable Scope Global vs Local By default, variables are global to your entire command prompt session.

Special Variables There are a few special situations where variables work a bit differently. Command Line Arguments to Your Script You can read the command line arguments passed to your script using a special syntax. You may not call a variable prior to defining it. Unlike other programming languages, in a batch file a variable is substituted by its actual value before the batch script is run.

In other words, the substitution is made when the script is read into memory by the command processor, not when the script is later run. This enables the use of variables as commands within the script, and as part of other variable names in the script, etc. The "script" in this context being a line - or block - of code, surrounded by round brackets:. In the above example, the ECHO command is evaluated as Hello when the script is read into memory, so the script will echo Hello forever, however many passes are made through the script.

The way to achieve the more "traditional" variable behaviour of the variable being expanded whilst the script is running is to enable "delayed expansion". This involves adding that command into the script prior to the loop instruction usually a FOR loop, in a batch script , and using an exclamation mark! Now, an advanced technique. Using the CALL command allows the batch command processor to expand a variable located on the same line of the script.

This can deliver multilevel expansion, by repeated CALL and modifier use. This is useful in, for example, a FOR loop.