Impertio-Studio docker-impl-go-templates
Quick Reference
Go Template Syntax Basics
| Syntax | Purpose | Example |
|---|---|---|
{{ .Field }} |
Access top-level field | {{ .State.Status }} |
{{ .Field.SubField }} |
Access nested field | {{ .NetworkSettings.IPAddress }} |
{{ json . }} |
Full JSON output | docker inspect --format='{{json .}}' |
{{ json .Field }} |
JSON for specific field | docker inspect --format='{{json .Config}}' |
table |
Table with headers | docker ps --format "table {{.Names}}\t{{.Status}}" |
\t |
Tab separator in tables | Used between columns |
{{ println }} |
Newline in output | Used inside range loops |
Template Functions
| Function | Purpose | Example |
|---|---|---|
json |
JSON-encode a value | {{ json .Config.Env }} |
join |
Join string slice with separator | {{ join .Config.Cmd " " }} |
upper |
Uppercase string | {{ upper .State.Status }} |
lower |
Lowercase string | {{ lower .State.Status }} |
title |
Title-case string | {{ title .State.Status }} |
split |
Split string by separator | {{ split .Image ":" }} |
println |
Print with newline | {{ println .Name }} |
index |
Access array/map element | {{ index .Config.Env 0 }} |
len |
Get length of array/map | {{ len .Config.Env }} |
Critical Warnings
NEVER use double quotes around the entire --format value when it contains Go template double quotes inside -- ALWAYS use single quotes for the outer wrapper on Linux/macOS. On Windows PowerShell, use escaped double quotes or backticks.
NEVER omit {{ end }} when using {{ if }} or {{ range }} -- every conditional and loop block MUST be closed with {{ end }}.
NEVER assume a field exists without checking -- use {{ if .Field }} to guard against nil values that cause template execution errors.
ALWAYS use {{ json .Field }} instead of trying to manually format complex nested objects -- JSON output is reliable and pipeable to jq.
ALWAYS use table prefix with \t separators for readable multi-column output -- omitting table removes column headers.
Conditionals
if / else / end
# Simple conditional
docker inspect --format='{{if .State.Running}}UP{{else}}DOWN{{end}}' myapp
# Check for empty value
docker inspect --format='{{if .State.Health}}{{.State.Health.Status}}{{else}}no healthcheck{{end}}' myapp
# Nested conditional
docker inspect --format='{{if eq .State.Status "running"}}HEALTHY{{else if eq .State.Status "exited"}}STOPPED{{else}}UNKNOWN{{end}}' myapp
Comparison Functions
| Function | Purpose | Example |
|---|---|---|
eq |
Equal | {{ if eq .State.Status "running" }} |
ne |
Not equal | {{ if ne .State.ExitCode 0 }} |
lt |
Less than | {{ if lt .State.ExitCode 1 }} |
le |
Less or equal | {{ if le .State.Pid 0 }} |
gt |
Greater than | {{ if gt .State.ExitCode 0 }} |
ge |
Greater or equal | {{ if ge .SizeRw 1000000 }} |
not |
Boolean negation | {{ if not .State.Running }} |
and |
Logical AND | {{ if and .State.Running .State.Health }} |
or |
Logical OR | {{ if or .State.Running .State.Paused }} |
Range Loops
Iterating Over Arrays
# Environment variables (one per line)
docker inspect --format='{{range .Config.Env}}{{println .}}{{end}}' myapp
# Mounts with source and destination
docker inspect --format='{{range .Mounts}}{{.Source}} -> {{.Destination}}{{println}}{{end}}' myapp
Iterating Over Maps
# Network names and IPs
docker inspect --format='{{range $net, $conf := .NetworkSettings.Networks}}{{$net}}: {{$conf.IPAddress}}{{println}}{{end}}' myapp
# Port bindings
docker inspect --format='{{range $port, $bindings := .NetworkSettings.Ports}}{{$port}} -> {{(index $bindings 0).HostPort}}{{println}}{{end}}' myapp
# All labels
docker inspect --format='{{range $k, $v := .Config.Labels}}{{$k}}={{$v}}{{println}}{{end}}' myapp
Index Function
# First element of an array
docker inspect --format='{{index .Config.Cmd 0}}' myapp
# Specific port binding
docker inspect --format='{{(index (index .NetworkSettings.Ports "80/tcp") 0).HostPort}}' myapp
# Label by key (with dot in name)
docker inspect --format='{{index .Config.Labels "com.example.version"}}' myapp
Format Patterns by Command
docker inspect -- Container State (6 patterns)
# 1. Container status
docker inspect --format='{{.State.Status}}' CONTAINER
# 2. Container PID
docker inspect --format='{{.State.Pid}}' CONTAINER
# 3. Container start time
docker inspect --format='{{.State.StartedAt}}' CONTAINER
# 4. Container exit code
docker inspect --format='{{.State.ExitCode}}' CONTAINER
# 5. Running boolean
docker inspect --format='{{.State.Running}}' CONTAINER
# 6. Health check status
docker inspect --format='{{if .State.Health}}{{.State.Health.Status}}{{else}}none{{end}}' CONTAINER
docker inspect -- Network Info (6 patterns)
# 7. IP address (first network)
docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' CONTAINER
# 8. MAC address
docker inspect --format='{{range .NetworkSettings.Networks}}{{.MacAddress}}{{end}}' CONTAINER
# 9. All networks with IPs
docker inspect --format='{{range $k,$v := .NetworkSettings.Networks}}{{$k}}={{$v.IPAddress}} {{end}}' CONTAINER
# 10. Gateway
docker inspect --format='{{range .NetworkSettings.Networks}}{{.Gateway}}{{end}}' CONTAINER
# 11. Port bindings (all)
docker inspect --format='{{range $p,$conf := .NetworkSettings.Ports}}{{$p}}->{{(index $conf 0).HostPort}} {{end}}' CONTAINER
# 12. Specific port mapping
docker inspect --format='{{(index (index .NetworkSettings.Ports "80/tcp") 0).HostPort}}' CONTAINER
docker inspect -- Configuration (6 patterns)
# 13. Image name
docker inspect --format='{{.Config.Image}}' CONTAINER
# 14. Entrypoint
docker inspect --format='{{json .Config.Entrypoint}}' CONTAINER
# 15. Command
docker inspect --format='{{json .Config.Cmd}}' CONTAINER
# 16. Environment variables
docker inspect --format='{{range .Config.Env}}{{println .}}{{end}}' CONTAINER
# 17. All labels as JSON
docker inspect --format='{{json .Config.Labels}}' CONTAINER
# 18. Specific label
docker inspect --format='{{index .Config.Labels "com.example.version"}}' CONTAINER
docker inspect -- Mounts & Size (4 patterns)
# 19. All mounts as JSON
docker inspect --format='{{json .Mounts}}' CONTAINER
# 20. Mount sources and destinations
docker inspect --format='{{range .Mounts}}{{.Source}} -> {{.Destination}}{{println}}{{end}}' CONTAINER
# 21. Log file path
docker inspect --format='{{.LogPath}}' CONTAINER
# 22. Root filesystem size (requires -s flag)
docker inspect --size --format='{{.SizeRootFs}}' CONTAINER
docker ps (4 patterns)
# 23. Compact table
docker ps --format "table {{.Names}}\t{{.Image}}\t{{.Status}}\t{{.Ports}}"
# 24. Names only
docker ps --format "{{.Names}}"
# 25. With specific label
docker ps --format "table {{.Names}}\t{{.Label \"app\"}}\t{{.Status}}"
# 26. JSON output (one object per line)
docker ps --format json
docker images (3 patterns)
# 27. Compact image list
docker images --format "table {{.Repository}}\t{{.Tag}}\t{{.Size}}"
# 28. Repository:tag pairs
docker images --format "{{.Repository}}:{{.Tag}}"
# 29. With digest
docker images --digests --format "table {{.Repository}}\t{{.Tag}}\t{{.Digest}}"
docker stats / network / volume / system (5 patterns)
# 30. Stats with custom columns
docker stats --no-stream --format "table {{.Name}}\t{{.CPUPerc}}\t{{.MemUsage}}\t{{.NetIO}}"
# 31. Network listing
docker network ls --format "table {{.Name}}\t{{.Driver}}\t{{.Scope}}"
# 32. Volume listing
docker volume ls --format "table {{.Name}}\t{{.Driver}}\t{{.Mountpoint}}"
# 33. System disk usage
docker system df --format "table {{.Type}}\t{{.TotalCount}}\t{{.Size}}\t{{.Reclaimable}}"
# 34. Docker info field
docker info --format '{{.ServerVersion}}'
Scripting Patterns
Extract Values for Shell Scripts
# Get container ID by name
CID=$(docker ps -qf "name=myapp")
# Get IP address into variable
IP=$(docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' myapp)
# Get host port for container port 80
PORT=$(docker inspect --format='{{(index (index .NetworkSettings.Ports "80/tcp") 0).HostPort}}' myapp)
# Get all running container names
docker ps --format "{{.Names}}" | while read name; do
echo "Container: $name"
done
# Get exit codes for all stopped containers
docker ps -a --filter status=exited --format "{{.Names}}: exit {{.Status}}"
Bulk Operations with Format Output
# Stop all containers on a specific network
docker network inspect --format='{{range .Containers}}{{.Name}} {{end}}' mynet | xargs docker stop
# Remove all images from a specific repository
docker images myrepo --format "{{.ID}}" | xargs docker rmi
# Get IPs of all running containers
docker ps -q | xargs -I {} docker inspect --format='{{.Name}}: {{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' {}
Decision Tree: Choosing Output Format
Need Docker command output?
├── Need full object details?
│ └── Use: docker inspect --format='{{json .}}' | jq
├── Need specific single field?
│ └── Use: --format='{{.Field.SubField}}'
├── Need readable multi-column table?
│ └── Use: --format "table {{.Col1}}\t{{.Col2}}"
├── Need machine-parseable output?
│ └── Use: --format json OR --format='{{json .Field}}'
├── Need to iterate nested data?
│ └── Use: --format='{{range .Items}}{{.Field}}{{println}}{{end}}'
└── Need conditional output?
└── Use: --format='{{if .Cond}}yes{{else}}no{{end}}'
Reference Links
- references/patterns.md -- 30+ format patterns organized by Docker command
- references/examples.md -- Complex template examples with conditionals, range loops, and scripting
- references/anti-patterns.md -- Common Go template mistakes and how to fix them