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% ".containerignore" "28" "Sep 2021" "" "Container User Manuals"
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# NAME
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.containerignore(.dockerignore) - files to ignore buildah or podman build context directory
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# INTRODUCTION
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Before container engines build an image, they look for a file named .containerignore or .dockerignore in the root
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context directory. If one of these file exists, the CLI modifies the context to exclude files and
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directories that match patterns specified in the file. This avoids adding them to images using the ADD or COPY
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instruction.
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The CLI interprets the .containerignore or .dockerignore file as a newline-separated list of patterns similar to
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the file globs of Unix shells. For the purposes of matching, the root of the context is considered to be both the
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working and the root directory. For example, the patterns /foo/bar and foo/bar both exclude a file or directory
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named bar in the foo subdirectory of PATH or in the root of the git repository located at URL. Neither excludes
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anything else.
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If a line in .containerignore or .dockerignore file starts with # in column 1, then this line is considered as a
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comment and is ignored before interpreted by the CLI.
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# EXAMPLES
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Here is an example .containerignore file:
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```
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# comment
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*/temp*
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*/*/temp*
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temp?
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```
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This file causes the following build behavior:
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Rule Behavior
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```
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# comment Ignored.
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*/temp* Exclude files and directories whose names start with temp in any immediate subdirectory of the root.
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For example, the plain file /somedir/temporary.txt is excluded, as is the directory /somedir/temp.
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*/*/temp* Exclude files and directories starting with temp from any subdirectory that is two levels below the
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root. For example, /somedir/subdir/temporary.txt is excluded.
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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.
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```
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Matching is done using Go’s filepath.Match rules. A preprocessing step removes leading and trailing whitespace and
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eliminates . and .. elements using Go’s filepath.Clean. Lines that are blank after preprocessing are ignored.
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Beyond Go’s filepath.Match rules, Docker also supports a special wildcard string ** that matches any number of
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directories (including zero). For example, **/*.go will exclude all files that end with .go that are found in all
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directories, including the root of the build context.
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Lines starting with ! (exclamation mark) can be used to make exceptions to exclusions. The following is an example .containerignore file that uses this mechanism:
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```
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*.md
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!README.md
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```
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All markdown files except README.md are excluded from the context.
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The placement of ! exception rules influences the behavior: the last line of the .containerignore that matches a
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particular file determines whether it is included or excluded. Consider the following example:
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```
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*.md
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!README*.md
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README-secret.md
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```
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No markdown files are included in the context except README files other than README-secret.md.
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Now consider this example:
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```
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*.md
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README-secret.md
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!README*.md
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```
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All of the README files are included. The middle line has no effect because !README*.md matches README-secret.md and
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comes last.
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You can even use the .containerignore file to exclude the Containerfile or Dockerfile and .containerignore files.
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These files are still sent to the daemon because it needs them to do its job. But the ADD and COPY instructions do
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not copy them to the image.
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Finally, you may want to specify which files to include in the context, rather than which to exclude. To achieve
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this, specify * as the first pattern, followed by one or more ! exception patterns.
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## SEE ALSO
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buildah-build(1), podman-build(1), docker-build(1)
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# HISTORY
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*Sep 2021, Compiled by Dan Walsh (dwalsh at redhat dot com) based on docker.com .dockerignore documentation.
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