Auto-uninstall old before installing new

2017-07-07T20:14:23Z

DavidWoods: Suggested code that does not assume previous install was in the default directory

{{PageAuthor|codehistorian}}

This is a code snippet you can put into your .onInit function that will detect whether your software is already installed and, if so, allows the user to uninstall it first.

In the source below, we use the define ${PROGRAM_NAME} to be the name of the product as well as the name of the installer/uninstaller. You can either define this define or search/replace it. If you name your uninstaller or registry location differently, you should change those strings accordingly.

<highlight-nsis>
Function .onInit

ReadRegStr $R0 HKLM \
"Software\Microsoft\Windows\CurrentVersion\Uninstall\${PROGRAM_NAME}" \
"UninstallString"
StrCmp $R0 "" done

MessageBox MB_OKCANCEL|MB_ICONEXCLAMATION \
"${PROGRAM_NAME} is already installed. $\n$\nClick `OK` to remove the \
previous version or `Cancel` to cancel this upgrade." \
IDOK uninst
Abort

;Run the uninstaller
uninst:
ClearErrors
ExecWait '$R0 _?=$INSTDIR' ;Do not copy the uninstaller to a temp file

IfErrors no_remove_uninstaller done
;You can either use Delete /REBOOTOK in the uninstaller or add some code
;here to remove the uninstaller. Use a registry key to check
;whether the user has chosen to uninstall. If you are using an uninstaller
;components page, make sure all sections are uninstalled.
no_remove_uninstaller:

done:

FunctionEnd
</highlight-nsis>

The following variant lets the uninstaller remove itself, so the IfErrors block is not needed any more:
<highlight-nsis>
Exec $INSTDIR\uninst.exe ; instead of the ExecWait line
</highlight-nsis>

NOTE: Both previous methods assume the program was installed in the default directory, which may not be correct. Here's what I use:

<highlight-nsis>
uninst:
ClearErrors
Exec $R0
done:
</highlight-nsis>

[[Category:System Related Functions]]

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Auto-uninstall old before installing new