---
title: How to fire a trigger only for certain products using a conditional expression
description: Set a condition on a trigger so it only fires when the job, shift or product matches a rule you define, using match regex to check text like an order description.
---
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# How to fire a trigger only for certain products using a conditional expression
## Set a condition on a trigger so it only fires when the job, shift or product matches a rule you define, using match regex to check text like an order description.
#### **What you'll build**
- A trigger that fires on every job start, but only when the product meets a condition you set.
- A condition that checks the text in a field, so one trigger covers a whole product group instead of a list of individual SKUs.
#### **Step 1 — Work out which products need the check**
Start with the outcome, not the rule. Take a plastic bottle check that only applies to PET products:
| Order description | Bottle type | Check needed? |
| --- | --- | --- |
| CHERRY-GLSBTL300 | Glass | No |
| CHERRY-PETBTL300 | PET | Yes |
| LIME-GLSBTL300 | Glass | No |
| LIME-PETBTL300 | PET | Yes |
The products that need the check all have `PET` somewhere in the order description. That shared piece of text is what the condition will look for.
#### **Step 2 — Open the trigger and turn on the conditional expression**
Any Job, Shift, State or Relay trigger can have a condition added. Open the trigger, go to the **Conditional Expression** tab, and switch **Enable Conditional Expression** to on.
The condition looks at the metadata for the job, shift or product. When the condition is true the trigger fires. When it is false, nothing happens.
#### **Step 3 — Build the condition**
The expression is built from three parts, left to right:
- The field you want to check, chosen from **Product Data** or **Special Fields**. In this example, `orderDescription`.
- The operator. In this example, **match regex**.
- The value to look for, entered under **Value**. In this example, `PET`.
Read the finished rule as a sentence: when the order description contains `PET`, the expression is true and the trigger fires.
#### **Step 4 — Save and check the trigger summary**
Save the trigger. The summary line at the top of the trigger window shows the trigger type, the timing and that a condition is applied, for example a job start trigger set to run after 1000 In, then every 1000 In, marked as conditional.
---
#### **What match regex is doing**
**match regex** works like the Find tool in a word processor: it searches the field for the text you give it. It is far more capable than a plain Find, because it matches a *pattern* rather than fixed text.
That matters when you do not know the exact value in advance. Compare these:
| Input | Expression | Match? |
| --- | --- | --- |
| CHERRY-GLSBTL300 | `PET` | No |
| CHERRY-PETBTL300 | `PET` | Yes |
| CHERRY-1GLSBTL330 | `\d{3}` | Yes |
| CHERRY-2GLSBTL650 | `\d{3}` | Yes |
In the last two rows, `\d` stands for any digit and `{3}` means three of them in a row. The pattern matches both codes even though the numbers differ.
A few patterns that cover most factory cases:
- `\d` any digit, `[A-Z]` any uppercase letter, `[A-Z0-9]` any uppercase letter or digit.
- `{3}` exactly three of the preceding item.
- `^` start of the text, `$` end of the text.
**Regex Cheat Sheet**
.png?width=670&height=1029&name=ofs-regex-cheatsheet%20(1).png)
---
#### **Adapting it to your own products**
- Swap `orderDescription` for whichever field carries the text you need to test. The fields available depend on the product data your site sends to OFS.
- Choose a piece of text that is present in every product that needs the check, and absent from every product that does not. If your product codes do not share a clean marker, add one to the product data rather than building a long expression.
- A condition can be added to Shift and State triggers the same way, so the same approach works for checks tied to a shift or a downtime state.
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