Working with parameters
A parameter is an input of a pipeline or workflow. You declare it once, use it like any other variable, and give it a different value every time the pipeline or workflow runs.
How parameters compare with fields and other variables is explained in Fields, parameters, and variables.
Declare a parameter
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Double-click an empty spot of the pipeline or workflow canvas to open its properties.
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On the Parameters tab, add a row for every parameter:
Column Description Parameter
The name of the parameter. You use it as
${NAME}.Default value
The value the parameter has when it is not given one. It can be empty, and it can contain other variables, for example
${PROJECT_HOME}/data/sample.csv.Description
A short explanation. It is shown next to the parameter when you run the pipeline or workflow from Hop Gui.
Use a parameter
When the pipeline or workflow starts, every parameter becomes a variable with the same name.
Use it as ${NAME} in any option that accepts variables, for example ${INPUT_FILE} as the file name of a Text file input transform.
A parameter always sets its variable, even when its value is empty. It hides a project, environment or other variable of the same name, unless that variable is used to give the parameter its value, as described below.
Give a parameter a value
From Hop Gui
When you run a pipeline or workflow, the Run Options dialog has two tabs:
- Parameters
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One row for every parameter, with its Default value and Description. Enter a value in the Value column, or leave it empty to use the default value. The Value column is empty every time the dialog opens: Hop Gui doesn’t remember the values of the previous run.
- Variables
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The variables the pipeline or workflow uses, other than its parameters, with their current value. Change a value to use another one for this run.
A parameter with an empty Value gets its default value, even when the project or the environment has a variable with the same name, or you add one on the Variables tab.
Preview and Debug open Run Options only when you click Configure. With Quick Launch, every parameter that has a default value gets it.
From hop-run
Pass parameters to hop-run with -p NAME=value.
Separate several parameters with commas.
Wrap a value that contains a comma in double quotes, and the whole option in single quotes so the shell keeps them:
./hop-run.sh -j my-project -r local -f '${PROJECT_HOME}/load-orders.hpl' \
-p 'INPUT_FILE=/data/orders.csv,COUNTRIES="BE,NL"'hop-run gives every parameter the first value it finds:
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The value passed with
-p. -
The value of a variable with the same name, for example a project or environment variable, or a system property passed with
-s. -
The default value.
An empty value, like -p INPUT_FILE=, gives the parameter its default value, even when a variable with the same name exists.
A name passed with -p that the pipeline or workflow doesn’t declare is set as a variable.
Unlike Hop Gui, hop-run uses a project or environment variable with the same name before the default value.
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From another pipeline or workflow
The Pipeline and Workflow actions, the Pipeline Executor and Workflow Executor transforms, and the other actions and transforms that start a pipeline or workflow have a Parameters tab. List a parameter of the child there with a value or a field, and it gets that value; otherwise it gets its default value, unless Pass parent values to matching parameters is enabled. The exact rules are in Passing parameters to a child pipeline or workflow.