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# Chapter 36. Parameters

Parameters are similar to constants/macros you can define once and use on various places in graph configuration.

Main benefits of parameters are centralization (later change the values only in one place) and configuration.

Every value, number, path, filename, attribute, etc. can be set up or changed with the help of parameters except `import` statement in CTL code.

Internal Parameters
External (Shared) Parameters
Graph Parameter Editor
Secure Graph Parameters
Parameters with CTL Expressions (Dynamic parameters)
Environment Variables
Canonicalizing File Paths
Using Parameters

| Important
Parameters cannot be used in `import` statement in CTL code.

#### Creating Parameters

Graph parameters can be created using Graph Parameter Editor or using Export As Graph Parameter button in Edit Component Dialog.

#### Parameter Name

The names of parameters may contain uppercase and lowercase letters (`A-Z,a-z`), digits (`0-9`) and the underscore character (`_`). Additionally, the name must not start with a digit.

Example 36.1. Parameter Name

`PARAMETER1` - valid parameter name

`My_Cool_Parameter_002` - valid parameter name

`127001` - invalid parameter name - begins with digit

`My parameter` - invalid parameter name - contains space character

`My-Great-Parameter` - invalid parameter name - contains hyphen character

`Bücher` - invalid parameter name - contains diacritics.

#### Priorities of Parameters

Graph parameters have lower priority than those specified in the Main tab or Parameters tab of Run Configurations.... In other words, both the internal and the external parameters can be overwritten by those specified in Run Configurations.... However, both the external and the internal parameters have higher priority than all environment variables and can overwrite them.

Each parameter can be created as:

- Internal: See Internal Parameters.

  Internal parameters can be Externalized: See Externalizing Internal Parameters.

- External (shared): See External (Shared) Parameters.

  External parameters can be Internalized: See Internalizing External (Shared) Parameters.

The value of parameters can be:

- Static - parameter contains a fixed string value

- Dynamic - parameter value is a CTL expression to be evaluated; see Parameters with CTL Expressions (Dynamic parameters)

Graph parameter editor is described in Graph Parameter Editor.

| Compatibility notice
CloverETL 3.5.x and later uses a new format of parameters different from CloverETL 3.4.x (and earlier). New CloverETL versions can read the old format and convert it to new format, but the new format is not compatible with older versions.

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