detect has already been installed

how to check previous version install when setup!

When you install, write the version number to the registry when done installing, e.g.

( slashes "/" should be backslashes "\" - darn php tag. )

WriteRegStr HKCU "Software/YourCompany/YourProduct/" "version" "version number" 

( above can be in the last section, or in .onInstSuccess, or.. etc.

Then when you run the installer, check for that value, e.g.

ReadRegStr $0 HKCU "Software/YourCompany/YourProduct/" "version" 

The version number will then be in $0. If the key did not exist, it'll just be empty. So you can do some rudimentary things with it...

StrCmp $0 "" _noPreviousInstall
IntCmp $0 current_version _sameVersion _olderVersion _newerVersion
_noPreviousInstall:
; insert code to execute here when there has been no previous installation.
goto _continue
_sameVersion:
; insert code to execute here when the old installed version is the same as the current version
goto _continue 
_olderVersion:
; insert code to execute here when the old installed version is older than the current version
goto _continue 
_newerVersion:
; insert code to execute here when the old installed version is /newer/ than the current version.
goto _continue 
_continue:
; the rest of the code to continue with 

Originally posted by Animaether
( slashes "/" should be backslashes "\" - darn php tag. )

Use the code tag instead.

haha.. yeah, we've been over this before (I was gone for a while) - I like the highlighting of PHP.

There should really be an NSIS tag added so syntax highlight while keeping the [code] formatting. I know, I know.. "will you write it?".. if I could! 🙂