How to evaluate if a environment variable is set in vimrc

Question

How to evaluate if an bash environment variable is set

for example

function! Myfoo(arg)
  if $SomeVar is set/exist ----> how to eval the SomeVar has been set
     ....
  endif
endfunction

Answer 1

You've (intuitively?) used the correct syntax; as :help expression-syntax explains (under :help expr-env ), the syntax is $VAR .

You can compare with an empty string ( if $SomeVar != "" ) or use empty() ( if !empty($SomeVar) ) to check whether a (non-empty) value has been supplied. It's not so easy to differentiate between empty environment variable and non-existing environment variable, so this is best avoided. (This distinction also is rarely used in shell scripts itself, neither.)