Linux Basic

Ok, I'll answer my own question 

Replacing specific string in file is very simple:
DIM content as String

' read the content of the file
content = File.Load("/path/to/file.ext")

'replace the string "old" with "new" (without quotes) in the content of the file
content = Replace$(content, "old", "new")

' save the new content to file
File.Save("/path/to/file.ext",content)This can be 2-lines code but I prefered to explain how it's done (or at least the way I figured out)

However, if you don't know the exact word you want to replace (you want to search for pattern match) things get complicated, here is the function I use now:
 PUBLIC FUNCTION Replace_Str(SrchFile AS String, SrchStr AS String, RpcStr AS String)
  DIM content_array AS String[]
  DIM sLine, content AS String
  DIM counter AS Integer
 
  ' load file content
  content = File.Load(SrchFile)
  ' split the content of the file to array with new line as delimiter
  content_array = Split(content, "\n")
 
  counter = 0
  ' read file line by line
  FOR EACH sLine IN content_array
    ' match pattern search agains SrchStr
    IF sLine LIKE SrchStr & "*" THEN
      ' save file content if SrchStr found and replace
      File.Save(SrchFile, Replace$(content, sLine, RpcStr))
     
      ' stop here, no need to search more (for me. to replace globaly remove BREAK)
      BREAK
    ENDIF
     
    counter += 1
  NEXT
 
' if the last lines was reached and still there wasn't match pop-up error message (remove if replacing globaly)
  IF counter = content_array.Count THEN
    Message.Error("Unable to find:\n\nString: " & SrchStr & "\n\n In: " & SrchFile)
  ENDIF
END
I hope this helps other Gambas users

More about pattern syntax : http://gambasdoc.org/help/doc/pcre

Cheers!

EDIT: If replacing globaly then exclude the error message too (noted in code)