Whitespace stripping behavior in Terraform template directives
Putting a tilde (~) at the beginning or end of Terraform template directives "consumes" whitespace. For example:
Users:
%{ for name in users ~}
${name},
%{~ endfor ~}
If users = ["alice", "bob"], this results in:
Users:
alice,bob,
While simple in theory, it can also be a little difficult to work with in practice. For example, if we add a space before ${name} like this:
Users:
%{ for name in users ~}
${name},
%{~ endfor ~}
Then the result is:
Users:
alice, bob,
You might expect the ~ at the end of %{ for name in users ~} to strip the space before ${name}, but it doesn't. This is because the ~ ONLY affects whitespace adjacent to the directive itself--not the whitespace inside the content lines.
Great, are empty lines also considered content lines then?
Users:
%{ for name in users ~}
${name},
%{~ endfor ~}
There should be 3 empty lines above me.
Nope, this results two empty lines following the ~}.
Users:
alice, bob,
There should be 3 empty lines above me.
That's because Terraform treats empty lines differently than other content, and removes ONLY the first empty line immediately before/after the directive.
TL;DR
%{~and~}trim whitespace and at most one empty line before/after the directive.- They do not remove any whitespace in non-empty lines before/after the directive.
- They only remove whitespace or empty lines directly next to the directive.