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The documentation for if/ifdef is slightly confusing. For <?if [expression] ?>, it states:
- Variables can be used to check for existence
...- If the variable doesn't exist, evaluation will fail and an error will be raised.
It turns out if you just go: <?if $(env.MY_VAR) ?> and MY_VAR is not defined, compilation will fail. How do I check for existence?
Ordinarily, this is where one would use an ifdef, but these work strangely in Wix too. Instead of using $(var.Variable) syntax, they use <?ifdef Variable?>, meaning environment variables can't be checked this way.
What do I need to do to get the equivalent of normal c pre-processor:
#ifdef MY_ENVIRONMENT_VARIABLE
in Wix?
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To display the values of environment variables, use the printenv command. If you specify the Name parameter, the system only prints the value associated with the variable you requested.
# Checking if an Environment Variable Exists in Python import os if 'USER' in os. environ: print('Environment variable exists! ') else: print('Environment variable does not exist. ') # Returns: # Environment variable exists!
To find out if a bash variable is empty: Return true if a bash variable is unset or set to the empty string: if [ -z "$var" ]; Another option: [ -z "$var" ] && echo "Empty" Determine if a bash variable is empty: [[ ! -z "$var" ]] && echo "Not empty" || echo "Empty"
The correct way to reference environment variables in ifdef sections is:
<?ifdef env.MY_VAR?>
...
<?endif?>
This works as expected.
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<Condition Message="Missing Environment Variable Message Goes Here"><![CDATA[%envvargoeshere]]></Condition>
Put the above element in the Package element of the wxs file. The installation will fail at runtime (install time) with a nice message if the environment variable does not exist.
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