I don't know of a way to do it with WMI, but you could use bcdedit in combination with Select-String:
$otherboot = bcdedit /enum |
Select-String "path" -Context 2,0 |
ForEach-Object { $_.Context.PreContext[0] -replace '^identifier +' } |
Where-Object { $_ -ne "{current}" }
Explanation:
The output of bcdedit /enum looks roughly like this:
Windows Boot Manager
--------------------
identifier {bootmgr}
device partition=\Device\HarddiskVolume1
description Windows Boot Manager
locale en-US
...
Windows Boot Loader
-------------------
identifier {current}
device partition=C:
path \Windows\system32\winload.exe
description Windows 7
locale en-US
...
Windows Boot Loader
-------------------
identifier {e0610d98-e116-11e1-8aa3-e57ee342122d}
device partition=C:
path \Windows\system32\winload.exe
description DebugEntry
locale en-US
...
The relevant sections of this output are the Windows Boot Loader sections, which – unlike the Windows Boot Manager section – have a path record. Thus we can use this record to select only the Windows Boot Loader sections:
Select-String "path"
Since the identifier records are 2 lines before the path records, we need 2 lines of PreContext (and no PostContext):
Select-String "path" -Context 2,0
Now we have selected the follwing two chunks from the output of bcdedit /enum:
identifier {current}
device partition=C:
path \Windows\system32\winload.exe
identifier {e0610d98-e116-11e1-8aa3-e57ee342122d}
device partition=C:
path \Windows\system32\winload.exe
Since we're only interested in the first line of the PreContext we select these 2 lines using a ForEach-Object loop:
ForEach-Object { $_.Context.PreContext[0] }
which reduces the two chunks to this:
identifier {current}
identifier {e0610d98-e116-11e1-8aa3-e57ee342122d}
from which we remove the category (identifier) via string replacement:
ForEach-Object { $_.Context.PreContext[0] -replace '^identifier +' }
The regular expression '^identifier +' matches a (sub)string starting with the word "identifier" followed by one or more spaces, which is replaced with the empty string. After this replacement the two chunks are reduced to this:
{current}
{e0610d98-e116-11e1-8aa3-e57ee342122d}
So now we only need to filter out the chunk containing {current} and what's left is the identifier of the other boot record:
Where-Object { $_ -ne "{current}" }
After this, the variable $otherboot contains the identifier of the not-current boot record.
