The Code Cave

This is a demonstration of how to use a TempFile in a .BAT or .CMD file. The goal of this example is to determine the relative path of the current working directory and assign it to a variable.

Concepts Demonstrated:

• Generating a unique file names


• Creating a temp file, using the Windows Naming convetion, and deleting it when done


• Calling support subroutines in a batch file


• Using GOTO :EOF to end exit a subroutine but not the batch file


• Use of the command line “FOR” routine


• Using Variables with “for /F”


• How to get the current directory


• Verbose and Quiet modes for a batch file

Temporary files are incredibly useful in batch files. When used in combination with a “For” loop, you can accomplish some amazing stuff from the command line.

In this example we assign a new file name to the TEMPORARY_FILE variable and then export the current working path to that file by echoing cd environment variable to it:

call :GETTEMPNAME
echo %cd%>%TEMPORARY_FILE%

Once our temp file has contents, the For routine can be used to parse each line and execute a command with the result. So, we use the For command to divide the working directory, lets say it is “C:\WorkingDir” into several peices (aka tokens):

FOR /F “tokens=1* delims=:” %%G IN (%TEMPORARY_FILE%) DO set RelativePath=%%H

Literaly we are telling it to break the line up at every colon ( : ), and to assign the first token to the variable %G. The asterisk (*) indicates that each token after that should be assigned to a new variable letter (H,I,J, and etc.). In our example, our %H will contain “\WorkingDir”.

“For /F” is really most usefull with larger files containing multiple lines. Since our file contains only one line with two tokens, the process stops there but you could, for example, parse all the names of files in a directory (dir *.xyz /b > %TEMPORARY_FILE%), or the contents of a registry key exported to that file using (REG QUERY [...] > %TEMPORARY_FILE%). I’ve used both of these methods in the past to do some really neat things that might have otherwise involved creating a custom executible. One advantage of doing it from teh command line is that it keeps the registry clean of all the garbage left behind by Windows anytime you run an exe.

Oh!

Something that is not often emphasized in “For /F” documentation is that it can parse variables as well as files. This could greatly optimize this example. Instead of parsing our file, we would simply put our %CD variable in quotes and call:

FOR /F “tokens=1* delims=:” %%G IN (”%CD%”) DO set RelativePath=%%H

We will get exactly the same results and can cut our batch file size in half! Of course, then we wouldn’t have a good example of temp file usage would we? So, we will do it the hard way.

Thus:

http://www.thecodecave.com/downloads/batch/GetRelativePath.bat