How do you add installation related computed strings to InnoSetup scripts?

Question

Currently when I upgrade a program I backup the existing files to a folder named backup in the program directory eg .

Source: "{app}\filename.exe"; DestDir: "{app}\backup"; Flags: external skipifsourcedoesntexist uninsneveruninstall

Is there a way to specify or compute a strings so the code is something like

Source: "{app}\filename.exe"; DestDir: "{app}\backup{date}"; Flags: external skipifsourcedoesntexist uninsneveruninstall

or combine a date with info on the previous version

Source: "{app}\filename.exe"; DestDir: "{app}\backup{previous version}{date}"; Flags: external skipifsourcedoesntexist uninsneveruninstall

Answer 1

Please read Pascal Scripting: Scripted Constants and Pascal Scripting: Support Functions Reference. Also read this and this. Anyway, this is how I did it:

[Dirs]
; create an empty folder...
Name: "{app}\{code:MyDateTimeString}"

[Code]
function MyDateTimeString(Param: String): String;
begin
  Result := GetDateTimeString('yyyy.mm.dd_hh.nn.ss', #0, #0);
end;

Answer 2

You can add runtime dynamic values using {code:...} constants.

An example of getting the current date and making a backup of the installation folder can be seen on the ISXKB wiki