if statement when environment variable exists/not exists in batch files -

i want check if environment variable set in pc. if yes x if not y.

i tried these , variations of them:

if exists %sign% runtest.exe --redirect -l %name% else runtest.exe -l %name%

if "%sign%" == "" runtest.exe --redirect -l %name% else runtest.exe -l %name%

none of them work in both cases (when environment variable sign exists , when doesn't exist).sometimes in 1 case...

please can help? thanks!

if conditionally perform command

if defined sign (      runtest.exe --redirect -l %name%  ) else (      runtest.exe -l %name% ) 

or shortly

if defined sign (runtest.exe --redirect -l %name%) else (runtest.exe -l %name%) 

valid syntax:

• all ), else , ( must on line follows: ) else (

note:

if defined return true if variable contains value (even if value space).

according above predicate, if defined sign condition seems equivalent reformulated test if not "%sign%"=="" valid in batch only, %undefined_variable% results empty string:

if not "%sign%"=="" (runtest.exe --redirect -l %name%) else (runtest.exe -l %name%) 

otherwise, in pure cli, %undefined_variable% results %undefined_variable%

proof:

==>type uv.bat @echo undefined_variable="%undefined_variable%"  ==>uv.bat undefined_variable=""  ==>echo undefined_variable="%undefined_variable%" undefined_variable="%undefined_variable%"  ==>