---
title: "Using template functions"
url: "https://axoflow.com/docs/axosyslog-core/4.28/chapter-manipulating-messages/customizing-message-format/template-functions/"
last_modified: "2023-07-02T20:37:04+02:00"
---

> For the complete documentation index, see [llms.txt](https://axoflow.com/docs/axosyslog-core/4.28/llms.txt).

# Using template functions

A template function is a transformation: it modifies the way macros or name-value pairs are expanded. Template functions can be used in template definitions, or when macros are used in the configuration of AxoSyslog. Template functions use the following syntax:

```shell
   $(function-name parameter1 parameter2 parameter3 ...)
```

For example, the `$(echo)` template function simply returns the value of the macro it receives as a parameter, thus `$(echo ${HOST})` is equivalent to `${HOST}`.

The parameters of template functions are separated by a whitespace character. A template function can have maximum 64 parameters. If you want to use a longer string or multiple macros as a single parameter, enclose the parameter in double-quotes or apostrophes. For example:

```shell
   $(echo "${HOST} ${PROGRAM} ${PID}")
```

Template functions can be nested into each other, so the parameter of a template function can be another template function, like:

```shell
   $(echo $(echo ${HOST}))
```

For details on the available template functions, see the descriptions of the individual template functions in [Template functions of AxoSyslog](https://axoflow.com/docs/axosyslog-core/4.28/chapter-manipulating-messages/customizing-message-format/reference-template-functions/index.md).

You can define your own template function as a regular configuration object (for example, to reuse the same function in different places in your configuration).

## Declaration:

```shell
   template-function <name-of-the-template-function> "<template-expression-using-strings-macros-template-functions>";
```

## Example: Using custom template functions

The following template function can be used to reformat the message. It adds the length of the message to the message template.

```shell
   template-function my-template-function "${ISODATE} ${HOST} message-length=$(length "${MSG}") ${MESSAGE}";
    destination d_file {
        file("/tmp/mylogs.log" template("$(my-template-function)\n"));
    };
```

You can also refer to existing templates in your template function.

```shell
   template my-custom-header-template "${ISODATE} ${HOST_FROM} ${MSGHDR}";
    template-function my-template-function "$(my-custom-header-template) message-length=$(length "${MESSAGE}") ${MESSAGE}";
```

Last modified July 2, 2023: [Change highlight mode of code examples (2f8a9593)](https://github.com/axoflow/axosyslog-core-docs/commit/2f8a95937c6498193e7168ce8b0dc831e9f0f8ad)