Slice and Dice Environment Variables

http://www.cherifrost.com/?tag=slap-chop

There are 2 types of environment variables and the options available for creating substrings on those variables are different.  Environment variables that are preceded with a single % sign are passed as arguments into the batch file or subroutine or from the FOR command.  Environment variables that are bracketed by % signs are created by the operating system or with the SET command.

OS and SET variables:

%var:str1=str2%	Replace "str1" with "str2" in %var%. If "str1" starts with "*" then replace text up to "str1"
%var:~a,b%	Substring "b" characters long starting at offset "a"
%var:~a%	Substring from character "a" to the end
%var:~-a%	Substring of the last "a" characters
%var:~a,-b%	Substring starting at "a" of all but the last "b" characters

Remember that the first character of the string is offset zero. So %var:~0% is the same as %var%.

Parameters and FOR variables:

%~X	remove quotes from var %X
%~fX	full path
%~dX	drive letter only
%~pX	path only
%~nX	file name only
%~xX	extension only
%~sX	short name
%~aX	attributes of file
%~tX	date/time of file
%~zX	size of file

Those dividers can be combined. So %~ftzaX will give a directory-like output for the variable %X showing the full path, date/time, size, and attributes.

All well and good but what about if you have a parameter variable from which you need a positional substring? Use the SET command to assign it to substringable variable.

SETLOCAL
SET X=%1
ECHO %X:~0,1%

This batch file will echo the first character of the string passed as the parameter.

What about the opposite case where you have a SET variable but you need to parse it as a file path?  I use a CALL statement to a subroutine which turns the variable back to a number parameter.

SETLOCAL
SET X=C:\windows\cmd.exe
CALL :Parse %X%

:Parse
ECHO %~d1 %~p1 %~n1 %~x1

The variable %X% becomes my %1 parameter in the subroutine, and I can parse that to get the drive, path, filename, and extension.

So let's put it all together to demo all the slapping and chopping. A couple of notes on the demo below. In the first part of the script the "&" lets you combine multiple commands on a single line. In this case I'm just adding a comment. (I prefer using "::" to make comments rather then the "REM" statement.) In the bottom part of the script I'm parsing the %0 variable which is the script file as its own parameter.

@ECHO Off
SETLOCAL
SET X=You're gonna love my nuts
ECHO %X:~13,4%   & :: Word in the middle
ECHO %X:~13%     & :: Words to the end
ECHO %X:~-7%     & :: Last 7 characters
ECHO %X:~7,-8%   & :: Skip first 7 and last 8 chars
ECHO %X:'= a%    & :: Replace apostrophe
ECHO.

ECHO Full path of this batch : %~f0
ECHO Drive letter            : %~d0
ECHO Relative path           : %~p0
ECHO Filename                : %~n0
ECHO Extension               : %~x0
ECHO Short name              : %~s0
ECHO File attributes         : %~a0
ECHO Date/time of last save  : %~t0
ECHO Size in bytes           : %~z0

http://www.dostips.com/  BTW, this guy has a bunch of cool tips and tricks if you get stuck having to work some complex batch files.

Commenters:  How else do you use substring capabilities for DOS environment variables?