问题
EDIT Hoping here to clarify my convoluted and misleading question... based on my mistaken assumption that -file accepts inputs. Thanks for setting me straight and pointing out that it's just a switch parameter; the inputs in my example actually get passed to -path. Sounds like that may be the fastest purely powershell way to search for multiple file types, since -filter accepts only a single input and -include is slower.
The get-childItem documentation says "Filters are more efficient than other parameters, because the provider applies them when retrieving the objects, rather than having Windows PowerShell filter the objects after they are retrieved."
v3 has a new parameter set with a -file parameter, probably meant for excluding directories, to match cmd.exe's dir /a:-d
Like -include and unlike -filter, -file accepts multiple, as in gci -file "*.ldf","*.bak"
So i'm wondering, and have thus far failed to reliably test, if -file is like -filter from a performance perspective, ie "more efficient", or more like the "other parameters" like -include. If -file is a filter, that's nice because afaict -filter only handles one filter at a time, so if you want multiple filters (like *.ldf and *.bak) then you need to either run gci -filter twice or use -include instead. So I'm wondering if -file lets us reap the efficiency benefits of a filter, for multiple filters.
I stumbled on some error text that's got me optimistic. The -file parameter wants -path to be the current directory, so this gci -path $path -file "*.bak","*.ldf" gives an error. Push-location seems like a viable workaround, but here I'm more interested in the content of the error text:
Get-ChildItem : Cannot convert 'System.Object[]' to the type 'System.String' required by parameter 'Filter'. Specified method is not supported.
I called -file but the error complains about "parameter 'Filter'". So maybe -file is efficient like a filter? OTOH, -filter doesn't need -path to be the current directory, so in that respect -file is more like -include.
回答1:
just one precision:
gci -path $path -file "*.bak","*.ldf"
-file is a switch parameter (as -directory is) and doesn't accept values (To get only files, use the File parameter and omit the Directory parameter. To exclude files, use the Directory parameter and omit the File parameter); then the "*.bak","*.ldf" are implicitly passed to -filter as value, and filter accept only string and not string[]. That's where your error came from.
Regarding performance: using -file or -directory is faster than using a where-object psiscontainer or ? { !$_.psiscontainer} because it's done at provider (filesystem in this case) level.
来源：https://stackoverflow.com/questions/13770262/is-get-childitems-new-file-parameter-fast-like-filter-or-slow-like-include