Match a regex pattern: regex_match

The regex_match template filter tests whether a string matches a regular expression (regex) pattern at the beginning of the string. A regular expression is a special text pattern that lets you describe what you are looking for, for example “any number” or “a word followed by a space”. It returns true if the beginning of the string matches the pattern, and false otherwise.

This is useful when you need to check whether a sensor value, entity ID, or other text starts with a specific pattern. For example, you might want to verify that a sensor value looks like a valid IP address, check if an entity ID starts with a certain prefix, or validate that an input follows an expected format. Because it only checks from the start of the string, use regex_search if you need to find a pattern anywhere in the text.

Usage

Here’s how to use this template function. Copy any example and adjust it to your setup.

{{ "light.living_room" | regex_match("light\\.") }}

true

Function signature

The signature is a technical summary of this template function. It shows the name of the function, the values (called parameters) it accepts, and what type of data each parameter expects (for example, a piece of text or a number).

Function parameters that have a = with a value after them are optional. If you leave them out, the default value shown is used automatically.

Function parameters without a = are usually required. A few optional parameters have no default value, so the signature shows them without a = as well. To check whether a parameter is required, look at the parameter list below the signature. Each parameter is marked as Required or Optional.

The most common optional parameter without a default value is default. The default parameter sets the value a function returns when the function can’t produce a result, for example, when float gets text that isn’t a number. If you leave out default, there is no fallback value, so most functions raise an error and the template fails. The parameter list of each function says what happens. If you set default, the function returns your value instead.

round(
    value: Any,
    precision: int = 0,
    method: str = "common",
    default: Any,
) -> float | int | Any

regex_match(
    value: str,
    find: str = "",
    ignorecase: bool = False,
) -> bool

Function parameters

The following parameters can be provided to this function.

Match vs search

regex_match only checks if the pattern matches at the beginning of the string. If you need to find a pattern anywhere in the string, use regex_search instead.

{{ "Room: Living Room" | regex_match("Living") }}
{{ "Room: Living Room" | regex_search("Living") }}

false
true

Case-insensitive matching

Set ignorecase to true to match regardless of upper or lowercase letters.

{{ "Light.living_room" | regex_match("light", ignorecase=true) }}

true

Good to know

• Only checks the start of the string. Use regex_search to match anywhere.
• A literal dot (.) must be escaped as \. because . matches any character in regex.

Try it yourself

Ready to test this? Open Settings > Tools > Template, paste the example into the Template editor, and watch the result update on the right. Edit the values to see how the function adapts to your own entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more].

More examples

Real scenarios where this function comes up in automations and templates. Copy any example and adapt it to your setup.

Check if an entity ID belongs to a domain

Verify that an entity ID starts with a specific domain prefix.

{% set entity = "sensor.outdoor_temperature" %}
{% if entity | regex_match("sensor\\.") %}
  This is a sensor entity
{% endif %}

This is a sensor entity

Validate a sensor value format

Check if a sensor value looks like a valid number with optional decimal point.

{{ states("sensor.temperature") | regex_match("^-?\\d+\\.?\\d*$") }}

true

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with your template and expected result, or share on our subreddit /r/homeassistant.

Related template functions

These functions work well alongside this one:

• Search for a regex pattern: regex_search - Searches for a regular expression pattern anywhere in a string.

• Replace using a regex pattern: regex_replace - Replaces all occurrences of a regular expression pattern in a string.

• Find all regex matches: regex_findall - Finds all occurrences of a regular expression pattern in a string and returns them as a list.

• Find regex match at index: regex_findall_index - Finds all occurrences of a regex pattern and returns the match at a specific index.

• Test if string matches pattern: match - Template test that checks if a string matches a regular expression at the beginning.