# IfVar

The `<IfVar>` element makes operations conditional on whether a variable exists and optionally matches a given value.

Using `<IfVar>` does not change the context (the current position in the document).

Attribute | Description
--- | ---
`containsRegex` | The variable must contain a match to this regular expression.
`matches` | The variable must match this value exactly.
`matchesRegex` | The variable must match this regular expression.
`negate` | Set this attribute to `true` to perform the child operations when the variable does not exist or does not match a given value.
`var` | The name of the variable to check.

The following example adds a field to the document metadata when the value of a variable named "reference" matches a regular expression.

    <FieldStandardization>
        <IfVar var="reference" matchesRegex="http.*">
            <AddField name="referenceUrl" value="$(reference)" />
        </IfVar>
    </FieldStandardization>

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