[batch] test for empty variable

nbrane May 22, 2010 at 20:55:06

my quite non-brilliant analysis is: 1) assuming you have set a value for %var% echoing that value to that value will result in a file, not a variable. f/e: set %var%=im_ok echo %var% > gives > %var% sends the string, "im_ok" to the line one of the file "im_ok", and not to a variable %var%. 2) Also, the intermediate pipe doesn't really do anything ( > gives > ). That file is not created, or not as a persistant entity. ultimately, the variable's value is reflected in a file having the name that is the variable's value. The value does not wind up back in the variable. It's in the file that has the variable's contents as its name. (f/e: you can: set aa=TEST but you can't: echo TEST > %aa% except %aa% is a file not a var. No reason to anyway.) Maybe post a synopsis of what you're trying to accomplish might get some real help as opposed to this non-help. :-) ps: sorry, just re-read my post. It IS saturday night, I HAVE consumed alc. beverages. apologies! Lol!

Wahine May 22, 2010 at 20:57:59

AFAIK an environment variable cannot be set to nothingness, it must contain at least one character or white space. If you use: Set var= Where one space follows the = you can test by using If "%var%"==" " echo something If you want to test for the existence of an environment variable use If defined %var% echo something or If Not defined %var% echo something Hope this helps.

Judago May 22, 2010 at 21:05:58

The first one should work, if %var% contains anything at all, including a space if will fail, especially if it contains double quotes. Perhaps: if not defined var echo empty Again if it contains anything at all...... I have no idea what you are trying to do with: echo %var% >gives> %var% It displays some interesting behaviour but nothing particularly useful. [edit] Gee I'm slow, beaten by minutes... @Wahine If you want to test a variable with "if [not] defined" you need to leave out the %'s or !'s otherwise it will check if the contents of the variable is itself a defined varable. To kill a variable you simply put nothing after the "=", "set var=" set var= [/edit]

biatche May 22, 2010 at 21:59:53

@echo off echo. if not defined %1 ( set /p drives=Enter drive to format [c, d, e, cd, cde]: ) else ( set drives=%1 ) rem if "%1"=="" ( set /p drives=Enter drive to format [c, d, e, cd, cde]: ) else ( set drives=%1 ) echo. echo drive %drives% if "%drives%"=="c" purandc c:\ -fg -s2c if "%drives%"=="d" purandc d:\ -fg -s2c if "%drives%"=="e" purandc e:\ -fg -s2c if "%drives%"=="cd" purandc c:\ d:\ -fg -s2c if "%drives%"=="cde" purandc c:\ d:\ e:\ -fg -s2c echo end the rem'd out part actually works.. but... if someone can test for me, set drives=%1 this doesn't seem to work.. actually it does both if and else produces the same result in echo drive %drives% but the else part doesn't get pass on to the next if statement i dont get it. oh yea i dont know how to make the if not defined %1 or 1 or whatever work.. haha .

Judago May 22, 2010 at 22:21:03

If not defined won't work for parameters or for variables, only environment variables. I added the "/i" switch to the if statement to make them case insensitive as well as a few other small changes: @echo off echo. :input if "%~1"=="" ( set drives= set /p drives=Enter drive to format [c, d, e, cd, cde]: if not defined drives goto input ) else ( set drives="%~1" ) set drives="%drives:"=%" if %drives%=="" goto input echo. echo drive %drives% if /I %drives%=="c" purandc c:\ -fg -s2c if /I %drives%=="d" purandc d:\ -fg -s2c if /I %drives%=="e" purandc e:\ -fg -s2c if /I %drives%=="cd" purandc c:\ d:\ -fg -s2c if /I %drives%=="cde" purandc c:\ d:\ e:\ -fg -s2c echo end

biatche May 23, 2010 at 03:30:44

thanks for all the help. got it working now .