Format command and log output

Table of contents

Docker supports Go templates which you can use to manipulate the output format of certain commands and log drivers.

Docker provides a set of basic functions to manipulate template elements. All of these examples use the docker inspect command, but many other CLI commands have a --format flag, and many of the CLI command references include examples of customizing the output format.

Note
When using the --format flag, you need to observe your shell environment. In a POSIX shell, you can run the following with a single quote:
$ docker inspect --format '{{join .Args " , "}}'
Otherwise, in a Windows shell (for example, PowerShell), you need to use single quotes, but escape the double quotes inside the parameters as follows:
$ docker inspect --format '{{join .Args \" , \"}}'

join

join concatenates a list of strings to create a single string. It puts a separator between each element in the list.

$ docker inspect --format '{{join .Args " , "}}' container

table

table specifies which fields you want to see its output.

$ docker image list --format "table {{.ID}}\t{{.Repository}}\t{{.Tag}}\t{{.Size}}"

json

json encodes an element as a json string.

$ docker inspect --format '{{json .Mounts}}' container

lower

lower transforms a string into its lowercase representation.

$ docker inspect --format "{{lower .Name}}" container

split

split slices a string into a list of strings separated by a separator.

$ docker inspect --format '{{split .Image ":"}}' container

title

title capitalizes the first character of a string.

$ docker inspect --format "{{title .Name}}" container

upper

upper transforms a string into its uppercase representation.

$ docker inspect --format "{{upper .Name}}" container

pad

pad adds whitespace padding to a string. You can specify the number of spaces to add before and after the string.

$ docker image list --format '{{pad .Repository 5 10}}'

This example adds 5 spaces before the image repository name and 10 spaces after.

truncate

truncate shortens a string to a specified length. If the string is shorter than the specified length, it remains unchanged.

$ docker image list --format '{{truncate .Repository 15}}'

This example displays the image repository name, truncating it to the first 15 characters if it's longer.

println

println prints each value on a new line.

$ docker inspect --format='{{range .NetworkSettings.Networks}}{{println .IPAddress}}{{end}}' container

Hint

To find out what data can be printed, show all content as json:

$ docker container ls --format='{{json .}}'