Powershell-如何从文本文件中获取前几行? [英] Powershell - how to obtain previous lines from text file?

问题描述

我有一个文本文件，其中包含数百行包含数据库信息的文本.

I have a text file containing hundreds of lines of text containing database info.

我正在尝试为任何35GB的数据库提取DatabaseId.

I'm trying to extract the DatabaseIds for any database which is 35GB.

我想使用Powershell询问该文件，并生成一个包含所有匹配数据库的文本文件.

I would like to interrogate the file using Powershell and produce a text file containing all the matching databases.

因此，从本质上讲，我想浏览文件，找到35的DatabaseSize，然后从前3行中提取相应的DatabaseId.

So in essence, I would like to scan through the file, find a DatabaseSize which is 35 and then extract the corresponding DatabaseId from 3 lines previous.

我看了遍整个网络，但似乎找不到能做到这一点的任何东西.

I've looked all over the net but can't seem to find anything which can do this.

文本文件摘录示例:

ServerId = VMlinux-b71655e1
DatabaseId = db-ecb2e784
Status = completed
LocationId = 344067960796
DatabaseSize = 30

ServerId = VMlinux-0db8d45b
DatabaseId = db-cea2f7a6
Status = completed
LocationId = 344067960796
DatabaseSize = 35

ServerId = VMlinux-c5388693
DatabaseId = db-9a421bf2
Status = completed
LocationId = 344067960796
DatabaseSize = 8

etc

推荐答案

尝试使用以下方法:

(( GC myfile.txt | 
   Select-String 'DatabaseSize = 35' -Context 3 ).context.precontext)[0]

如果有多个匹配项:

(GC myfile.txt | 
SELECT-STRING 'DATABASESIZE = 35' -Context 3 ) | % { ($_.context.precontext)[0] }

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