I would like to select any one ".xls" file in a directory. The problem is the dir command can return different types.
我想在目录中选择任何一个“.xls”文件。问题是dir命令可以返回不同的类型。
gci *.xls
will return
将返回
- object[] if there is more than one file
- object []如果有多个文件
- FileInfo if there is exactly one file
- 如果只有一个文件，则为FileInfo
- null if there are no files
- 如果没有文件，则返回null
I can deal with null, but how do I just select the "first" file?
我可以处理null，但是如何选择“第一个”文件呢？
1 个解决方案
#1
86
You can force PowerShell into returning an array, even when only one item is present by wrapping a statement into @(...):
您可以通过将语句包装到@（...）中来强制PowerShell返回一个数组，即使只有一个项目存在：
@(gci *.xls)[0]
will work for each of your three cases:
将适用于您的三种情况：
- it returns the first object of a collection of files
- 它返回文件集合的第一个对象
- it returns the only object if there is only one
- 如果只有一个，它返回唯一的对象
- it returns
$nullof there wasn't any object to begin with - 它返回$ null，没有任何对象开始
There is also the -First parameter to Select-Object:
Select-Object还有-First参数：
Get-ChildItem -Filter *.xls | Select-Object -First 1
gci -fi *.xls | select -f 1
which works pretty much identical to the above, except that the list of files doesn't need to be enumerated completely by Get-ChildItem, as the pipeline is aborted after the first item. This can make a difference when there are many files matching the filter.
与上面的工作方式完全相同，除了文件列表不需要由Get-ChildItem完全枚举，因为管道在第一个项目之后被中止。当有许多文件与过滤器匹配时，这会有所不同。
#1
86
You can force PowerShell into returning an array, even when only one item is present by wrapping a statement into @(...):
您可以通过将语句包装到@（...）中来强制PowerShell返回一个数组，即使只有一个项目存在：
@(gci *.xls)[0]
will work for each of your three cases:
将适用于您的三种情况：
- it returns the first object of a collection of files
- 它返回文件集合的第一个对象
- it returns the only object if there is only one
- 如果只有一个，它返回唯一的对象
- it returns
$nullof there wasn't any object to begin with - 它返回$ null，没有任何对象开始
There is also the -First parameter to Select-Object:
Select-Object还有-First参数：
Get-ChildItem -Filter *.xls | Select-Object -First 1
gci -fi *.xls | select -f 1
which works pretty much identical to the above, except that the list of files doesn't need to be enumerated completely by Get-ChildItem, as the pipeline is aborted after the first item. This can make a difference when there are many files matching the filter.
与上面的工作方式完全相同，除了文件列表不需要由Get-ChildItem完全枚举，因为管道在第一个项目之后被中止。当有许多文件与过滤器匹配时，这会有所不同。