Returns a text string with every occurrence of searchString in text replaced by replaceString in text.
text - any text expression or text field
searchString - any text expression or text field
replaceString - any text expression or text field
Data type returned 
Originated in 
FileMaker Pro 6.0 or earlier
This function is case-sensitive. Compare to the Replace function.
Multiple substitutions are allowed when you enclose each pair of searchString and replaceString parameters within square brackets [ ] and separate them with semicolons. FileMaker supports up to 999 nested substitute conditions. Each search and replace list item is also separated by semicolons. For example:
Substitute(text; [search1; replace1]; [search2; replace2]; ... [searchN; replaceN])
Substitute(Description;“WYSIWYG.”;“What you see is what you get.”) replaces every occurrence of the acronym “WYSIWYG.” in the Description field with the phrase What you see is what you get.
Substitute(text;[“a”;“A”];[“b”;“B”]) replaces every lowercase a or b with A or B.
Related topics 
Functions reference (category list)
Functions reference (alphabetical list)
About formulas
About functions
Defining calculation fields
Using operators in formulas