Question

I’m being driven crazy by a stupidly simple problem that is eating up my time. I just want to append strings separated by comma, but the comma doesn’t get appended. Below is my batch file snippet:

set MissingParams=
set SwitchURL=
set TrustStore=
if 0%SwitchURL%==0 (set MissingParams=SwitchURL)
  if 0%TrustStore%==0 (
    if not 0%MissingParams%==0 (        
         set MissingParams=%MissingParams%,
      )
      set MissingParams=%MissingParams%TrustStore
  )

After runnin this script when I echo %MisingParams%, the expected value is SwitchURL,TrustStore but it simply prints

SwitchURLTrustStore.

D:\deleteme>echo %MissingParams%
SwitchURLTrustStore

For debugging, when I introduced some echo statements in the batch file, the results are even more bizzare:

set MissingParams=
if 0%SwitchURL%==0 (set MissingParams=SwitchURL)
  if 0%TrustStore%==0 (
    if not 0%MissingParams%==0 (    
      echo MissingParams=%MissingParams%
      set MissingParams=%MissingParams%,
      echo MissingParams=%MissingParams%
    )
    set MissingParams=%MissingParams%TrustStore
    echo MissingParams=%MissingParams%
  )

When I run the above script it prints

MissingParams=SwitchURL
MissingParams=SwitchURL
MissingParams=SwitchURL

And when I echo the value from the command prompt, as before I get SwitchURLTrustStore

D:\deleteme>echo %MissingParams%
SwitchURLTrustStore

Does anyone have any ideas? This is frustrating me to no end.

Answer 1

This is the standard parenthesis/delayedExpansion problem.

The simple rule is %var% are expanded before a parenthesis block is executed(while parsing).

If you need the var-expansion later, you should use the delayed expansion.
Explained in set /?

setlocal EnableDelayedExpansion
set MissingParams=
set SwitchURL=
set TrustStore=
if 0!SwitchURL!==0 (set MissingParams=SwitchURL)
  if 0!TrustStore!==0 (
    if not 0!MissingParams!==0 (        
         set MissingParams=!MissingParams!,
      )
      set MissingParams=!MissingParams!TrustStore
  )