Capture the command's standard error stream to a file written to
the designated output directory.
If stderr is a string, it specifies the file name to use.
If stderr is an expression, the expression is evaluated and must
return a string with the file name to use to capture stderr. If the
return value is not a string, or the resulting path contains illegal
characters (such as the path separator /) it is an error.
Capture the command's standard error stream to a file written to the designated output directory. If stderr is a string, it specifies the file name to use. If stderr is an expression, the expression is evaluated and must return a string with the file name to use to capture stderr. If the return value is not a string, or the resulting path contains illegal characters (such as the path separator /) it is an error.