Select-String and Grep
Dustin Marx has a blog entry where he compares Unix/Linux, PowerShell and DOS commands. In it he says, "If there is one Unix command I would love to have in PowerShell, it is the grep command with its regular expression support." Well Dustin, your wish is our command. Select-String command to be precise:
PS> Get-Help Select-String
NAME
Select-String
SYNOPSIS
Identifies patterns in strings.
SYNTAX
Select-String [-pattern] <string[]> -inputObject <psobject> [-include <stri
ng[]>] [-exclude <string[]>] [-simpleMatch] [-caseSensitive] [-quiet] [-lis
t] [<CommonParameters>]
Select-String [-pattern] <string[]> [-path] <string[]> [-include <string[]>
] [-exclude <string[]>] [-simpleMatch] [-caseSensitive] [-quiet] [-list] [<
CommonParameters>]
DETAILED DESCRIPTION
Identifies patterns in strings. By default, Select-String interprets the va
lue of the Pattern parameter as a regular expression and matches input agai
nst it. To learn more about regular expressions in Windows PowerShell, type
get-help about_regular_expression. You can suppress the regular expression
match by using the SimpleMatch parameter. A simple match attempts to find
the string specified in the Pattern parameter as a substring of the input.
The cmdlet makes it easy to search string content from files. It includes a
Path parameter that supports wildcards and when that parameter is used, th
e contents of the referenced files are retrieved and matched against the va
lue of the Pattern parameter.
Output from the cmdlet is, by default, a MatchInfo object which includes de
tailed information about the matches. The information is most useful when t
he input to the cmdlet is retrieved from files. The object includes propert
ies like Filename and Line, which have the value 'InputStream' when the inp
ut was not from a file. You can use the Quiet parameter to suppress the out
put of MatchInfo objects. In that case, the resulting output becomes a bool
ean value that is true if a match occurred and false otherwise.
When matching file content, you can use the List parameter to stop after th
e first match in each input file. You should use this parameter if you only
require a single match, because it will result in faster matching commands.
There are a ton of great scenarios but here are some of the more common usages:
PS> dir . -recurse |%{ "`n*** $($_.name)"; cat $_}
*** animals.txt
dog
cat
horse
cow
*** fruit.txt
orange
apple
cherry
*** trees.txt
Elm
Maple
Oak
Dogwood
Apple
PS> Set-Alias ss Select-String
PS> ss Dog *
animals.txt:1:dog
trees.txt:4:Dogwood
PS> ss Dog * -CaseSensitive
trees.txt:4:Dogwood
PS> ss ^[cd]o *
animals.txt:1:dog
animals.txt:4:cow
trees.txt:4:Dogwood
PS> ss ^[cd]o -path * -Exclude *an*.txt
trees.txt:4:Dogwood
We've expanded Select-String in the next version with a number of additional functions. One of my favorites is -Context which allows you to specify the number of lines you want displayed before and after a match. Check it out:
PS> ss oak *
trees.txt:3:Oak
PS> ss oak * -Context 1,0
trees.txt:2:Maple
> trees.txt:3:Oak
PS> ss oak * -Context 0,1
> trees.txt:3:Oak
trees.txt:4:Dogwood
PS> ss oak * -Context 2,1
trees.txt:1:Elm
trees.txt:2:Maple
> trees.txt:3:Oak
trees.txt:4:Dogwood
And last but not least, this is PowerShell so of course we are not going to just emit text, we emit objects which
PS> ss dog * |fl *
IgnoreCase : True
LineNumber : 1
Line : dog
Filename : animals.txt
Path : C:\temp\ss\animals.txt
Pattern : dog
IgnoreCase : True
LineNumber : 4
Line : Dogwood
Filename : trees.txt
Path : C:\temp\ss\trees.txt
Pattern : dog
We should have produced an alias from grep to Select-String.
Enjoy!
Jeffrey Snover [MSFT]
Windows Management Partner Architect
Visit the Windows PowerShell Team blog at: http://blogs.msdn.com/PowerShell
Visit the Windows PowerShell ScriptCenter at: http://www.microsoft.com/technet/scriptcenter/hubs/msh.mspx