Is this from a specific release onwards? Is it worth calling that out?

Kind of; it’s 1.3.x for this specific behavior, but it was similar before.

I can annotate it.

On Oct 27, 2014, at 1:46 PM, James Turnbull [email protected] wrote:

In docs/sources/reference/builder.md:

@@ -104,6 +104,33 @@ be treated as an argument. This allows statements like:
Here is the set of instructions you can use in a Dockerfile for building
images.

+### Environment Replacement
Is this from a specific release onwards? Is it worth calling that out?

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It's not at all clear to me what env. vars are being compared to here. Similarly to what?

similarly to how they were handled in prior to 1.3?

On Oct 27, 2014, at 3:25 PM, Fred Lifton [email protected] wrote:

In docs/sources/reference/builder.md:

@@ -104,6 +104,37 @@ be treated as an argument. This allows statements like:
Here is the set of instructions you can use in a Dockerfile for building
images.

+### Environment Replacement (as of 1.3)
+
+Note: prior to 1.3, Dockerfile environment variables were handled
+similarly, but not exactly the same -- there was no formal definition at the
It's not at all clear to me what env. vars are being compared to here. Similarly to what?

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Not sure we want or need this version information. The docs are versioned, so we should just describe the behavior in the current version. If we want to to broadcast the change, I'd suggest we use release notes for that.

OK. You guys need to figure this out — which style is best -- and get back to me.

On Oct 27, 2014, at 3:30 PM, Fred Lifton [email protected] wrote:

In docs/sources/reference/builder.md:

@@ -104,6 +104,37 @@ be treated as an argument. This allows statements like:
Here is the set of instructions you can use in a Dockerfile for building
images.

+### Environment Replacement (as of 1.3)
Not sure we want or need this version information. The docs are versioned, so we should just describe the behavior in the current version. If we want to to broadcast the change, I'd suggest we use release notes for that.

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Ah, sorry. I didn't see @jamtur01 's comments from earlier. Didn't mean to send a mixed message. I think this is good enough to ship now, I'll label it for later editing.

Nothing to stop this from being merged, but reading this, I wonder why and perhaps this needs some extra clarification; is this by design? Not implemented (yet)? Not supported because of possible security implications?

A bit of explanation may prevent needless support tickets and/or discussions.

There are too many sandboxing issues with environment replacement — I made a semi-executive decision to exclude them for now.

On Oct 27, 2014, at 4:14 PM, Sebastiaan van Stijn [email protected] wrote:

In docs/sources/reference/builder.md:

• WORKDIR ${foo} # WORKDIR /bar
• ADD . $foo # ADD . /bar
• COPY $foo /quux # COPY $foo /quux

+The instructions that handle environment variables in the Dockerfile are:
+
+* ENV
+* ADD
+* COPY
+* WORKDIR
+* EXPOSE
+* VOLUME
+* USER
+
+ONBUILD instructions are NOT supported for environment replacement, even
+the instructions above.
Nothing to stop this from being merged, but reading this, I wonder why and perhaps this needs some extra clarification; is this by design? Not implemented (yet)? Not supported because of possible security implications?

A bit of explanation may prevent needless support tickets and/or discussions.

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Think its worth it to mention that in layman's terms (because of the reasons mentioned)?

Leave that decision up to you and the doc maintainers :)

on what --> as to which. Missed it before, sorry.

Fixed.

On Oct 27, 2014, at 4:27 PM, Fred Lifton [email protected] wrote:

In docs/sources/reference/builder.md:

@@ -104,6 +104,46 @@ be treated as an argument. This allows statements like:
Here is the set of instructions you can use in a Dockerfile for building
images.

+### Environment Replacement
+
+Note: prior to 1.3, Dockerfile environment variables were handled
+similarly, in that they would be replaced as described below. However, there
+was no formal definition on what instructions handled environment replacement
on what --> as to which. Missed it before, sorry.

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