get ranges inside formula

Use range.getFormula() to get the formula and then use regex with String.match to get the cells:

/*<ignore>*/console.config({maximize:true,timeStamps:false,autoScroll:false});/*</ignore>*/ 
const f =
  '=page1!C2:C*0,8+page2!B29*0,15+page3!C144*0,056+sheet1!c:c* Sheet56!D10:D-D5:G10';
const matched = f.match(/(\w+!)?[A-Za-z]+\d*(:[A-Za-z]+\d*)?/g);
console.log(JSON.stringify(matched));

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• (\w+!)? - [?optional]Matches one or more word followed by ! for sheet name(eg: page1!)
• [A-Za-z]+\d* - Matches one or more letters [A-Z] followed by zero or more digits \d* for range string(eg: C2)
• (:[A-Za-z]+\d*)? - [optional] another range string match preceded by a :(eg: :C50)

Description

Here is an sample script that can parse equations as shown into the reference cells.

Note this only works for the specific formula you specified.

Code.gs

function test() {
  try {
    let spread = SpreadsheetApp.getActiveSpreadsheet();
    let sheets = spread.getSheets().map( sheet => sheet.getName() );
    // for this test
    sheets = ["page1","page2","page3"];
    let sheet = spread.getSheetByName("Sheet1");
    let formula = sheet.getRange("A1").getFormula();
    console.log(formula);
    // break into parts
    let parts = formula.split("*");  // but notice this is for specific case of *
    parts.pop() // the last part doesn't contain any cell reference
    console.log(parts);
    let i = 0;
    let results = [];
    parts.forEach( part => {  let j = sheets.findIndex( sheet => part.indexOf(sheet) >= 0 )
                              // remove sheet from range
                              let k = part.split('!')[1];  // this give cell A1 notation
                              results.push(sheets[j]+k)
                           }
                  );
    console.log(results);
  }
  catch(err) {
    console.log(err);
  }
}

Execution log

6:54:44 AM  Notice  Execution started
6:54:46 AM  Info    =page1!C2*0,8+page2!B29*0,15+page3!C144*0,05
6:54:46 AM  Info    [ '=page1!C2', '0,8+page2!B29', '0,15+page3!C144' ]
6:54:46 AM  Info    [ 'page1C2', 'page2B29', 'page3C144' ]
6:54:45 AM  Notice  Execution completed

Reference

• Array.map
• Range.getFormula()
• String.split()
• Array.pop()
• Array.forEach()
• Array.findIndex()