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Add note to docs about lack of shell processing in JSON form 

Closes #5509

Signed-off-by: Doug Davis <dug@us.ibm.com>
This commit is contained in:
Doug Davis 2014-10-02 11:16:51 -07:00
parent f69a262464
commit 98ceae1a84
1 changed files with 26 additions and 5 deletions
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31
docs/sources/reference/builder.md
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@ -170,7 +170,7 @@ generated images.
RUN has 2 forms:
- `RUN <command>` (the command is run in a shell - `/bin/sh -c`)
- `RUN <command>` (the command is run in a shell - `/bin/sh -c` - *shell* form)
- `RUN ["executable", "param1", "param2"]` (*exec* form)
The `RUN` instruction will execute any commands in a new layer on top of the
@ -193,6 +193,13 @@ commands using a base image that does not contain `/bin/sh`.
> The *exec* form is parsed as a JSON array, which means that
> you must use double-quotes (") around words not single-quotes (').
> **Note**:
> Unlike the *shell* form, the *exec* form does not invoke a command shell.
> This means that normal shell processing does not happen. For example,
> `CMD [ "echo", "$HOME" ]` will not do variable substitution on `$HOME`.
> If you want shell processing then either use the *shell* form or execute
> a shell directly, for example: `CMD [ "sh", "-c", "echo", "$HOME" ]`.
The cache for `RUN` instructions isn't invalidated automatically during
the next build. The cache for an instruction like
`RUN apt-get dist-upgrade -y` will be reused during the next build. The
@ -216,9 +223,9 @@ The cache for `RUN` instructions can be invalidated by `ADD` instructions. See
The `CMD` instruction has three forms:
- `CMD ["executable","param1","param2"]` (like an *exec*, this is the preferred form)
- `CMD ["executable","param1","param2"]` (*exec* form, this is the preferred form)
- `CMD ["param1","param2"]` (as *default parameters to ENTRYPOINT*)
- `CMD command param1 param2` (as a *shell*)
- `CMD command param1 param2` (*shell* form)
There can only be one `CMD` instruction in a `Dockerfile`. If you list more than one `CMD`
then only the last `CMD` will take effect.
@ -237,6 +244,13 @@ instruction as well.
> The *exec* form is parsed as a JSON array, which means that
> you must use double-quotes (") around words not single-quotes (').
> **Note**:
> Unlike the *shell* form, the *exec* form does not invoke a command shell.
> This means that normal shell processing does not happen. For example,
> `CMD [ "echo", "$HOME" ]` will not do variable substitution on `$HOME`.
> If you want shell processing then either use the *shell* form or execute
> a shell directly, for example: `CMD [ "sh", "-c", "echo", "$HOME" ]`.
When used in the shell or exec formats, the `CMD` instruction sets the command
to be executed when running the image.
@ -446,9 +460,9 @@ The copy obeys the following rules:
ENTRYPOINT has two forms:
- `ENTRYPOINT ["executable", "param1", "param2"]`
(like an *exec*, the preferred form)
(*exec* form, the preferred form)
- `ENTRYPOINT command param1 param2`
(as a *shell*)
(*shell* form)
There can only be one `ENTRYPOINT` in a `Dockerfile`. If you have more
than one `ENTRYPOINT`, then only the last one in the `Dockerfile` will
@ -488,6 +502,13 @@ optional but default, you could use a `CMD` instruction:
> The *exec* form is parsed as a JSON array, which means that
> you must use double-quotes (") around words not single-quotes (').
> **Note**:
> Unlike the *shell* form, the *exec* form does not invoke a command shell.
> This means that normal shell processing does not happen. For example,
> `CMD [ "echo", "$HOME" ]` will not do variable substitution on `$HOME`.
> If you want shell processing then either use the *shell* form or execute
> a shell directly, for example: `CMD [ "sh", "-c", "echo", "$HOME" ]`.
> **Note**:
> It is preferable to use the JSON array format for specifying
> `ENTRYPOINT` instructions.