Usage

The simplest usage of gomplate is to just replace environment variables. All environment variables are available by referencing .Env (or getenv) in the template.

The template is read from standard in, and written to standard out.

Use it like this:

$ echo "Hello, {{ .Env.USER }}" | gomplate
Hello, hairyhenderson

Commandline Arguments

`--config`

Specify the path to a gomplate config file. The default is .gomplate.yaml. Can also be set with the GOMPLATE_CONFIG environment variable.

For example:

$ cat myconfig.yaml
in: hello {{ .data.thing }}

datasources:
  data:
    url: https://example.com/data.json
$ gomplate --config myconfig.yaml
hello world

`--file`/`-f`, `--in`/`-i`, and `--out`/`-o`

By default, gomplate will read from Stdin and write to Stdout. This behaviour can be changed.

Use --file/-f to use a specific input template file. The special value - means Stdin.
Use --out/-o to save output to file. The special value - means Stdout.
Use --in/-i if you want to set the input template right on the commandline. This overrides --file. Because of shell command line lengths, it’s probably not a good idea to use a very long value with this argument.

Multiple inputs

You can specify multiple --file and --out arguments. The same number of each much be given. This allows gomplate to process multiple templates slightly faster than invoking gomplate multiple times in a row.

`--input-dir` and `--output-dir`

For processing multiple templates in a directory you can use --input-dir and --output-dir together. In this case all files in input directory will be processed recursively as templates and the resulting files stored in --output-dir. The output directory will be created if it does not exist and the directory structure of the input directory will be preserved.

You can use the --exclude argument and/or a .gomplateignore file to exclude some of the files in the input directory.

Example:

# Process all files in directory "templates" with the datasource given
# and store the files with the same directory structure in "config"
gomplate --input-dir=templates --output-dir=config --datasource config=config.yaml

`--output-map`

Sometimes a 1-to-1 mapping betwen input filenames and output filenames is not desirable. For these cases, you can supply a template string as the argument to --output-map. The template string is interpreted as a regular gomplate template, and all datasources and external nested templates are available to the output map template.

A new context is provided, with the input filename is available at .in, and the original context is available at .ctx. For convenience, any context keys not conflicting with in or ctx are also copied.

All whitespace on the left or right sides of the output is trimmed.

For example, given an input directory in/ containing files with the extension .yaml.tmpl, if we want to rename those to .yaml:

$ gomplate --input-dir=in/ --output-map='out/{{ .in | strings.ReplaceAll ".yaml.tmpl" ".yaml" }}'

Referencing complex output map template files

It may be useful to store more complex output map templates in a file. This can be done with external templates.

Consider a template out.t:

{{- /* .in may contain a directory name - we want to preserve that */ -}}
{{ $f := filepath.Base .in -}}
out/{{ .in | strings.ReplaceAll $f (index .filemap $f) }}.out

And a datasource filemap.json:

{ "eins.txt": "uno", "deux.txt": "dos" }

We can blend these two together:

$ gomplate -t out=out.t -c filemap.json --input-dir=in --output-map='{{ template "out" . }}'

`--chmod`

By default, output files are created with the same file mode (permissions) as input files. If desired, the --chmod option can be used to override this behaviour, and set the output file mode explicitly. This can be useful for creating executable scripts or ensuring write permissions.

The value must be an octal integer in the standard UNIX chmod format, i.e. 644 to indicate that owner gets read+write, group gets read-only, and others get read-only permissions. See the chmod(1) man page for more details.

Note: --chmod is supported on Windows, but only read/write (666) and read-only (444). If you pass a value like 755 on Windows, gomplate will reinterpret that as what you probably intended (read-write).

`--exclude` and `--include`

When using the --input-dir argument, it can be useful to filter which files are processed. You can use --exclude and --include to achieve this. The --exclude flag takes a .gitignore-style pattern, and any files matching the pattern will be excluded. The --include flag is effectively the opposite of --exclude. You can also repeat the arguments to provide a series of patterns to be excluded/included.

Patterns provided with --exclude/--include are matched relative to the input directory.

Note: These patterns are not treated as filesystem globs, and so a pattern like /foo/bar.json will match relative to the input directory, not the root of the filesystem as they may appear!

Examples:

$ gomplate --exclude example/** --exclude *.png --input-dir in/ --output-dir out/

This will stop all files in the in/example directory from being processed, as well as all .png files in the in/ directory.

$ gomplate --include *.tmpl --exclude foo*.tmpl --input-dir in/ --output-dir out/

This will cause only files ending in .tmpl to be processed, except for files with names beginning with foo: template.tmpl will be included, but foo-template.tmpl will not.

`--exclude-processing`

When using the --input-dir argument, it can be useful to skip some files from processing and copy them directly to the output directory. Like the --exclude flag, it takes a .gitignore-style pattern, and any files match the pattern will be copied.

Note: These patterns are not treated as filesystem globs, and so a pattern like /foo/bar.json will match relative to the input directory, not the root of the filesystem as they may appear!

Examples:

$ gomplate --exclude-processing `*.png` --input-dir in/ --output-dir out/

This will skip all *.png files in the in/ directory from being processed, and copy them to the out/ directory.

`.gomplateignore` files

You can also use a file named .gomplateignore containing one exclude pattern on each line. This has the same syntax as a .gitignore file. When processing sub-directories, .gomplateignore files in the parent directory are also considered. Patterns are matched relative to the location of the .gomplateignore file.

`--datasource`/`-d`

Add a data source in name=URL form. Specify multiple times to add multiple sources. The data can then be used by the datasource and include functions.

Data sources referenced in this way are lazy-loaded: they will not be read until the template is parsed and a datasource or include function is encountered.

See Datasources for full details.

A few different forms are valid:

mydata=file:///tmp/my/file.json
- Create a data source named mydata which is read from /tmp/my/file.json. This form is valid for any file in any path.
mydata=file.json
- Create a data source named mydata which is read from file.json (in the current working directory). This form is only valid for files in the current directory.
mydata.json
- This form infers the name from the file name (without extension). Only valid for files in the current directory.

`--datasource-header`/`-H`

Provides one (or more) HTTP headers to be sent along with the matching HTTP-based datasource. Value is in the form alias="HeaderName: header-value".

Note that the alias does not need to map to a datasource specified in a command-line flag, but can be used in dynamically-defined datasources (see defineDatasource).

`--context`/`-c`

Add a data source in name=URL form, and make it available in the default context as .<name>. The special name . (period) can be used to override the entire default context.

Data sources referenced with --context will be immediately loaded before gomplate processes the template. This is in contrast to the --datasource behaviour, which lazy-loads data while processing the template.

All other rules for the --datasource/-d flag apply.

Examples:

$ gomplate --context post=https://jsonplaceholder.typicode.com/posts/2 -i 'post title is: {{ .post.title }}'
post title is: qui est esse

$ gomplate -c .=http://xkcd.com/info.0.json -i '<a href="{{ .img }}">{{ .title }}</a>'
<a href="https://imgs.xkcd.com/comics/diploma_legal_notes.png">Diploma Legal Notes</a>

`--missing-key`

Control the behavior during execution if a map is indexed with a key that is not present in the map.

Available values:

error (default): Execution stops immediately with an error.
default or invalid: Do nothing and continue execution. If printed, the result is the string "<no value>".
zero: The operation returns the zero value for the element (which may be nil, in which case the string "<no value>" is printed).

Examples:

$ gomplate --missing-key error -i 'Hi {{ .name }}'
Hi 14:06:57 ERR  error="failed to render template <arg>: template: <arg>:1:6: executing \"<arg>\" at <.name>: map has no entry for key \"name\""

$ gomplate --missing-key default -i 'Hi {{ .name }}'
Hi <no value>

$ gomplate --missing-key zero -i 'Hi {{ .name | default "Alex" }}'
Hi Alex

$ gomplate --missing-key zero -i 'Hi {{ .name | required }}'
Hi 14:12:04 ERR  error="failed to render template <arg>: template: <arg>:1:11: executing \"<arg>\" at <required>: error calling required: can not render template: a required value was not set"

Overriding the template delimiters

Sometimes it’s necessary to override the default template delimiters ({{/}}). Use --left-delim/--right-delim or set $GOMPLATE_LEFT_DELIM/$GOMPLATE_RIGHT_DELIM.

`--template`/`-t`

Add a nested template or directory of templates that can be referenced by the main input template(s) with the template built-in or the functions in the tmpl namespace. Specify multiple times to add multiple template references.

Similar to data sources, the value is a alias=url pair, where alias is the template name and url is an optionally-relative URL to the template file or directory. Note that currently only file: URLs are supported.

In addition to the alias=url form, in certain cases the alias may be omitted, in which case the url will be used as the alias. When referencing a directory, all files in the directory will be included, available to be referenced as alias/<filename>.

Some examples:

--template foo=file:///tmp/foo.tmpl

References a file /tmp/foo.tmpl

It will be available as a template named foo:

$ gomplate --template foo=file:///tmp/foo.tmpl -i 'here are the contents of the template: [ {{ template "foo" }} ]'
here are the contents of the template: [ hello, world! ]

--template mytemplate.t

References a file mytemplate.t in the current working directory.

It will be available as a template named mytemplate.t:

$ gomplate --template helloworld.tmpl -i 'here are the contents of the template: [ {{ template "helloworld.tmpl" }} ]'
here are the contents of the template: [ hello, world! ]

--template path/to/mytemplate.t

References a file mytemplate.t in the path path/to/.

It will be available as a template named path/to/mytemplate.t:

$ gomplate --template foo/bar/helloworld.tmpl -i 'here are the contents of the template: [ {{ template "foo/bar/helloworld.tmpl" }} ]'
here are the contents of the template: [ hello, world! ]

--template path/to/

Makes available all files in the path path/to/.

Any files within this path can be referenced:

$ gomplate --template foo/bar/ -i 'here are the contents of the template: [ {{ template "foo/bar/helloworld.tmpl" }} ]'
here are the contents of the template: [ hello, world! ]

--template alias=path/to/mytemplate.t

References a file mytemplate.t in the path path/to/

It will be available as a template named alias:

$ gomplate --template t=foo/bar/helloworld.tmpl -i 'here are the contents of the template: [ {{ template "t" }} ]'
here are the contents of the template: [ hello, world! ]

--template alias=path/to/

Makes available all files in the path path/to/.

Any files within this path can be referenced, with the path replaced with alias:

$ gomplate --template dir=foo/bar/ -i 'here are the contents of the template: [ {{ template "dir/helloworld.tmpl" }} ]'
here are the contents of the template: [ hello, world! ]

`--plugin`

See the config file for more plugin configuration options.

Some specialized use cases may need functionality that gomplate isn’t capable of on its own. If you have a command or script to perform this functionality, you can plug in your own custom functions with the --plugin flag:

$ gomplate --plugin echo=/bin/echo -i 'Hello {{ echo "World" }}'
Hello World

All arguments provided to the function will be passed as positional arguments to the plugin, and the plugin’s standard output stream (Stdout) will be printed to the rendered output. To instead pipe the final argument of the function to the plugin’s standard input stream, use the config file and set the pipe field.

If the plugin exits with a non-zero exit code, gomplate will also fail. All signals caught by gomplate will be propagated to the plugin. Any output on the standard error stream will be printed to gomplate’s standard error stream.

Plugins can also be written as PowerShell or CMD scripts (.ps1, .bat, or .cmd extensions) on Windows.

By default, plugins will time out after 5 seconds. To adjust this, set the GOMPLATE_PLUGIN_TIMEOUT environment variable to a valid duration such as 10s or 3m, or use the pluginTimeout configuration option.

`--exec-pipe`

When using post-template command execution, it may be useful to pipe gomplate’s rendered output directly into the command’s standard input.

To do this, simply use --exec-pipe instead of --out or any other output flag:

$ gomplate -i 'hello world' --exec-pipe -- tr a-z A-Z
HELLO WORLD

Note that multiple inputs are not yet supported when using this option.

`--experimental`

Use this flag to enable experimental functionality. See the docs for the experimental configuration option for more information.

`--verbose`

When you specify --verbose, gomplate will log some extra information useful for debugging and troubleshooting.

All log output is done on the standard error stream, and so will never interrupt rendered output. For example, redirecting output to a file or another command will work as expected, without the log output interfering.

Log formatting

The GOMPLATE_LOG_FORMAT environment variable can be used to control the format of the log messages that gomplate may output, whether error messages or debug messages when the --verbose option is in use.

The value can be set to json, logfmt, console, or simple.

`json` format

json is the default format when gomplate is used in a script or non-interactive terminal.

$ GOMPLATE_LOG_FORMAT=json gomplate -i '{{'

{"level":"error","error":"template: <arg>:1: unexpected unclosed action in command","time":"2021-01-24T20:49:02-05:00"}

`console` format

console is the default format used when gomplate is used in an interactive terminal. Messages are printed in colour when possible.

$ GOMPLATE_LOG_FORMAT=console gomplate -i '{{'

20:49:28 ERR  error="template: <arg>:1: unexpected unclosed action in command"

`logfmt` format

logfmt format is a simple structured key=value format.

$ GOMPLATE_LOG_FORMAT=logfmt bin/gomplate -i '{{'

time=2021-01-24T20:50:58-05:00 level=error  error="template: <arg>:1: unexpected unclosed action in command"

`simple` format

simple omits the level and timestamp for a very simplistic output.

$ GOMPLATE_LOG_FORMAT=simple bin/gomplate -i '{{'

 error="template: <arg>:1: unexpected unclosed action in command"

Post-template command execution

Gomplate can launch other commands when template execution is successful. Simply add the command to the command-line after a -- argument:

$ gomplate -i 'hello world' -o out.txt -- cat out.txt
hello world

See also --exec-pipe for piping output directly into the post-exec command.

Suppressing empty output

Sometimes it can be desirable to suppress empty output (i.e. output consisting of only whitespace). To do so, set suppressEmpty: true in your config file, or GOMPLATE_SUPPRESS_EMPTY=true in your environment:

$ export GOMPLATE_SUPPRESS_EMPTY=true
$ gomplate -i '{{ print "   \n" }}' -o out
$ cat out
cat: out: No such file or directory

Usage

Commandline Arguments

--config

--file/-f, --in/-i, and --out/-o

Multiple inputs

--input-dir and --output-dir

--output-map

Referencing complex output map template files

--chmod

--exclude and --include

--exclude-processing

.gomplateignore files

--datasource/-d

--datasource-header/-H

--context/-c

--missing-key

Overriding the template delimiters

--template/-t

--plugin

--exec-pipe

--experimental

--verbose

Log formatting

json format

console format

logfmt format

simple format

Post-template command execution

Suppressing empty output

`--config`

`--file`/`-f`, `--in`/`-i`, and `--out`/`-o`

`--input-dir` and `--output-dir`

`--output-map`

`--chmod`

`--exclude` and `--include`

`--exclude-processing`

`.gomplateignore` files

`--datasource`/`-d`

`--datasource-header`/`-H`

`--context`/`-c`

`--missing-key`

`--template`/`-t`

`--plugin`

`--exec-pipe`

`--experimental`

`--verbose`

`json` format

`console` format

`logfmt` format

`simple` format