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% ".containerignore" "5" "Sep 2021" "" "Container User Manuals"
# NAME
.containerignore(.dockerignore) - files to ignore buildah or podman build context directory
# INTRODUCTION
Before container engines build an image, they look for a file named
`.containerignore` or `.dockerignore` in the root context directory. If one of
these file exists, the CLI modifies the context to exclude files and
directories that match patterns specified in the file. This avoids adding them
to images using the ADD or COPY instruction.
The CLI interprets the `.containerignore` or `.dockerignore` file as a
newline-separated list of patterns similar to the file globs of Unix
shells. For the purposes of matching, the root of the context is considered to
be both the working and the root directory. For example, the patterns `/foo/bar`
and `foo/bar` both exclude a file or directory named bar in the foo subdirectory
of PATH or in the root of the git repository located at URL. Neither excludes
anything else.
If a line in `.containerignore` or `.dockerignore` file starts with `#` in
column 1, then this line is considered as a comment and is ignored before
interpreted by the CLI.
# EXAMPLES
Here is an example `.containerignore` file:
```
# comment
*/temp*
*/*/temp*
temp?
```
This file causes the following build behavior:
Rule Behavior
```
# comment Ignored.
*/temp* Exclude files and directories whose names start with temp in any immediate subdirectory of the root.
For example, the plain file /somedir/temporary.txt is excluded, as is the directory /somedir/temp.
*/*/temp* Exclude files and directories starting with temp from any subdirectory that is two levels below the
root. For example, /somedir/subdir/temporary.txt is excluded.
temp? Exclude files and directories in the root directory whose names are a one-character extension of temp. For example, /tempa and /tempb are excluded.
```
Matching is done using the golang `path/filepath` package.
Match rules:
* A preprocessing step removes leading and trailing whitespace and eliminates
. and .. elements using the golang `path/filepath` package.
* Lines that are blank after preprocessing are ignored.
Beyond the `filepath.Match` rules, Docker also supports a special wildcard
string `**` that matches any number of directories (including zero). For
example, `**/*.go` will exclude all files that end with `.go` that are found in
all directories, including the root of the build context.
Lines starting with `!` (exclamation mark) can be used to make exceptions to
exclusions. The following is an example .containerignore file that uses this
mechanism:
```
*.md
!README.md
```
All markdown files except README.md are excluded from the context.
The placement of `!` exception rules influences the behavior: the last line of
the `.containerignore` that matches a particular file determines whether it is
included or excluded. Consider the following example:
```
*.md
!README*.md
README-secret.md
```
No markdown files are included in the context except README files other than README-secret.md.
Now consider this example:
```
*.md
README-secret.md
!README*.md
```
All of the README files are included. The middle line has no effect because
`!README*.md` matches `README-secret.md` and comes last.
You can even use the .containerignore file to exclude the `Containerfile` or
`Dockerfile` and `.containerignore` files. These files are still sent to the
daemon because it needs them to do its job. But the `ADD` and `COPY` instructions
do not copy them to the image.
Finally, you may want to specify which files to include in the context, rather
than which to exclude. To achieve this, specify `*` as the first pattern,
followed by one or more `!` exception patterns.
## SEE ALSO
buildah-build(1), podman-build(1), docker-build(1)
# HISTORY
*Sep 2021, Compiled by Dan Walsh (dwalsh at redhat dot com) based on docker.com .dockerignore documentation.
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