I would like to search for a pattern in bunch of source files. The pattern should act as a marker. If the pattern is found, I would like to process that line by performing a substitution of another string

**For example:**

```
Private const String myTestString = @"VAL15"; // STRING—REPLACE-VAL##

```

Here, I want to search my source file for pattern `STRING—REPLACE-VAL` and then replace `VAL15` with `VAL20` in same. 

**Output:**

```
private const String myTestString = @"VAL20"; // STRING—REPLACE-VAL##

```

Tried below command but not working as expected.

```
sed -i  '/,STRING—REPLACE-VAL##/ {; s/,VAL15,/,VAL20,/;}' myTestFile.cpp

```

**Question:** Is it possible to search for `STRING—REPLACE-VAL##` and then search for matching pattern `@"VAL`??" in same line and replace 15 by 20.

`sed` supports search & replacing the same pattern very easily but not sure if `sed` supports to search pattern but replace another string in the matching line?

Any help would be appreciated. Thanks in advance.