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In transformations that support use of regex patterns, you may need to specify capture groups. A capture group is a pattern that describes a set of one or more characters that constitute a match.

These patterns are described using regular expression syntax. implements a version of regular expressions based off of RE2 and PCRE regular expressions.

This section contains information on how special capture group references are managed.

Dollar sign in replace transform

The dollar sign ($) is used as a form of escape character in the with parameter of the replace transform. This pattern identifies the replacement string.

In the table below, you can review how these replacement patterns are supported across the running environments.

Pattern	Description	On Photon	On Hadoop
`$$`	Inserts a `$` in the replacement value.	Yes	Yes
`$n` or `$nn`	For non-negative digits `n`, this pattern inserts the nth parameterized sub-match string, provided that the first argument was a regex object.	Yes	Yes

Examples

In the following example, the MyColumn column contains the value foobar in all rows.

source value replace transform replacement

foobar

replace col:MyColumn with:'$$f' on:'f'

$foobar

foobar

replace col:MyColumn with:'$2' on:`(f)(o)(o)bar`

Note that the on parameter is a .