Is it possible to conditionally add a file/folder to NSIS installer - nsis

Question

Is it possible to conditionally add a file/folder and installation option to a NSIS installer?
My idea is that if the folder Foo exists at a given location it should be added to the installer and the option to install Foo should be added to the installer as well. But if the folder Foo does not exist, the NSIS script should just create the installer but leave Foo and the option to select Foo out of it.

Answer 1

You can try to include a file with /NONFATAL. If it exists, it will be included by the compiler. In runtime, you can check if installer was able to extract it.
File /NONFATAL "file.zip"
${If} ${FileExists} "$OUTDIR\file.zip"
...
${EndIf}

Answer 2

In NSIS 2 File /NONFATAL /R "c:\foo" is the best you can do without external tools and you need a little hack to hide the section when there are no files:
!include LogicLib.nsh
Page Components
Page InstFiles
Section "Main"
SetOutPath $InstDir
# File "C:\myfiles\myapp.exe"
SectionEnd
Section "Install Foo" SID_FOO
SetOutPath $InstDir
File /NONFATAL /r "C:\myfiles\foo\*.*"
SectionEnd
Function .onInit
SectionGetSize ${SID_FOO} $0
StrCmp $0 0 "" +3
SectionSetFlags ${SID_FOO} 0 ; Force all flags off including the checkmark
SectionSetText ${SID_FOO} "" ; Hide the section because its size is 0
FunctionEnd
If this is unacceptable you can use !system and get a little help from cmd.exe to check if something exists:
!tempfile INCEXIST
!system 'if exist "C:\myfiles\foo\*.*" echo !define HAVE_FOO > "${INCEXIST}"'
!include "${INCEXIST}"
!delfile "${INCEXIST}"
!ifdef HAVE_FOO
Section "Install Foo"
SetOutPath $InstDir
File /r "C:\myfiles\foo\*.*"
SectionEnd
!endif
In NSIS 3 !if supports a /FileExists switch:
!if /FileExists "C:\myfiles\foo\*.*"
Section "Install Foo"
SetOutPath $InstDir
File /r "C:\myfiles\foo\*.*"
SectionEnd
!endif

Answer 3

Example to replace file what depends on running service and exists or not at targget location
IfFileExists "$SYSDIR\my_file.dll" exist notexist
exist:
ExecWait 'net stop desired_service'
SetOutPath $SYSDIR
SetOverwrite on
File "/oname=$SYSDIR\my_file.dll" "Path to my file\my_file.dll"
ExecWait 'net start desired_service'
notexist:
.....what you want to do if doesn't exists