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

--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 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 not currently supported on Windows. Behaviour is undefined, but will likely not change file permissions at all.

--exclude

When using the --input-dir argument, it can be useful to exclude certain files from being processed. You can use --exclude to achieve this. It takes a .gitignore-style pattern, and any files matching the pattern will be excluded. You can also repeat the argument to provide a series of patterns to be excluded.

Patterns provided with --exclude 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!

Example:

$ 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.

.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.

--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>

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 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.

A few different forms are valid:

  • --template mytemplate.t
    • References a file mytemplate.t in the current working directory.
    • It will be available as a template named mytemplate.t: console $ 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: console $ 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: console $ 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: console $ 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: console $ 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! ]

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

Suppressing empty output

Sometimes it can be desirable to suppress empty output (i.e. output consisting of only whitespace). To do so, set 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