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String Replacement Usage

Consider the following Custom Namespace.Image Removed

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usage usage

String Replacement Usage

The String Conversion feature can be used in any Custom Namespace or in the Sparkplug B Namespace. The String Replacement feature supports the following.

• Replacements are executed using the 'Order Index' order from lowest to highest.
• Single character to single character replacement
• String to string replacement
• Character or string to nothing (i.e. removes a string or character)
• Regular Expression (regex) to string, character, or nothing replacement (i.e. uses a regex for pattern matching rather than a literal string)
• Character replacements will only occur for characters that will be part of the tag path. Character replacements are not applied to Ignition tag values
• Null or empty replacement string

Examples:

• Remove all '@' symbols
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• Replace all '@' symbols with '_'
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• Replace all 'abc' character sequences with 'def'
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• Replace all characters between the literal strings 'start' and 'end' with a '_' character using a regex
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Replacement Replacement

How do I determine what string replacement I need?

When an Ignition tag is created, there are some rules that need to be followed:

• The first character of the Tag name must be one of the following:
  • Letter - specifically, a letter as recognized by Unicode's Letter (L) category.
  • Number
  • Underscore
• The second character, and every character after that can then be one of the following:
  • Letter
  • Number
  • Underscore
  • Space
  • Any of the following special characters: ', -, :, (, )

To determine the string replacement needed for the namespace:

• Look at the published MQTT topic and a sample payload, if parsing as JSON, and identify any characters that may be problematic.
• Review these characters against the rules above or open Ignition designer and test if a tag can be created with the specific characters.
• If a tag cannot be created, created a string replacement rule.

Consider Now consider an incoming MQTT message with the characteristics:

• Topic = a/b
• Payload = { "tag 1": 123, "tag@2": "some.value" }

This A custom namespace with a subscription a/# will be able to receive the message however this will fail to be handled by the Custom Namespace and an error will be logged that looks like:

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This tells MQTT Engine that for this custom namespace, convert any '@' characters that would normally be part of the tag path to '_' characters. So now when we publish the same MQTT message, we don't get an error message and the tag gets properly created as shown below with the '@' character replaced by a '_' character.

The String Conversion feature can be used in any Custom Namespace or in the Sparkplug B Namespace. The String Replacement feature supports the following.

• Replacements are executed using the 'Order Index' order from lowest to highest.
• Single character to single character replacement
• String to string replacement
• Character or string to nothing (i.e. removes a string or character)
• Regular Expression (regex) to string, character, or nothing replacement (i.e. uses a regex for pattern matching rather than a literal string)
• Character replacements will only occur for characters that will be part of the tag path. Character replacements are not applied to Ignition tag values
• Null or empty replacement string

Examples:

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