Using custom functions (FileMaker Pro Advanced)
To create a custom function:
1.
In FileMaker Pro Advanced, choose File menu > Manage > Custom Functions.
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In the Edit Custom Function dialog box, for Function Name, type a name for the new function.
Custom function names must be unique and cannot exceed 100 characters.
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5.
If the formula requires parameters, for Function Parameters, type the parameter name and click Plus Add button. You can edit or delete a parameter name by selecting it in the list and clicking Edit Edit button or Delete Delete button.
6.
 
For Operators, choose an operator from the list.
You can also type parameter names, operators, and functions in the Edit Custom Function dialog box instead of using the lists or keypad.
7.
All accounts is the default option for Availability and allows all users of the current database to see and use the custom function. If you want the custom function to be available only to those with Full Access privileges, select Only accounts assigned full access privileges.
8.
Click OK to close the Edit Custom Function dialog box.
9.
Continue creating custom functions, or click OK to close the Manage Custom Functions dialog box.
To change, duplicate, or delete a custom function:
1.
Choose File menu > Manage > Custom Functions.
2.
 
For Function Name, select the custom function and click Edit. In the Edit Custom Function dialog box, make your changes, then click OK.
For Function Name, select the custom function and click Duplicate.
For Function Name, select the custom function and click Delete.
3.
To copy a custom function to another FileMaker Pro file:
1.
Choose File menu > Manage > Custom Functions.
2.
Tip  You can press Ctrl-click (Windows) or Command-click (OS X) to select non-contiguous functions, or press Shift-click to select contiguous functions.
3.
Tip  OS X: You can choose File menu > Copy to copy a selected function.
4.
5.
Choose File menu > Manage > Custom Functions.
6.
Tip  OS X: You can choose File menu > Paste to paste a selected function.
The custom function you copied appears at the bottom of the list. If FileMaker Pro determines this function is invalid in the context of the target file (for example, a dependent function, field, or calculation is missing from the target file or the function contains an invalid field type reference), the pasted function is enclosed in comment characters (/*<function_definition>*/). For more information, see Custom Function dependency rules (FileMaker Pro Advanced).
7.
Notes
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If you do not have Full Access privileges and attempt to edit a calculation that uses a custom function restricted to Full Access accounts, you see the string <Private Function> instead of the custom function. You cannot change the calculation as long as the <Private Function> declaration appears in the formula.
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Related topics 
About custom functions (FileMaker Pro Advanced)
Importing custom functions (FileMaker Pro Advanced)
Functions reference (category list)
Functions reference (alphabetical list)