问题
I have been using regex to parse text within some XML nodes. However, when I use -SimpleMatch with Select-String, the MatchInfo object doesn't appear to contain any matches.
I am unable to find anything online that indicates this behavior is normal. I am now wondering if it is my Powershell installation. (For reference: the computer I'm using has Powershell 3.0 installed.)
Using a very simple example, we can return the expected MatchInfo Object when using the regex patterning:
PS H:\> $c = "abd 14e 568" | Select-String -Pattern "ab"
PS H:\> $c.Matches
Groups : {ab}
Success : True
Captures : {ab}
Index : 0
Length : 2
Value : ab
But adding the -SimpleMatch parameter appears to not return the Matches property in the MatchInfo object:
PS H:\> $c = "abd 14e 568" | Select-String -Pattern "ab" -SimpleMatch
PS H:\> $c.Matches
PS H:\>
Piping $c to Get-Member confirms a MatchInfo Object was returned:
PS H:\> $c | gm
TypeName: Microsoft.PowerShell.Commands.MatchInfo
Name MemberType Definition
---- ---------- ----------
Equals Method bool Equals(System.Object obj)
GetHashCode Method int GetHashCode()
GetType Method type GetType()
RelativePath Method string RelativePath(string directory)
ToString Method string ToString(), string ToString(string directory)
Context Property Microsoft.PowerShell.Commands.MatchInfoContext Context {get;set;}
Filename Property string Filename {get;}
IgnoreCase Property bool IgnoreCase {get;set;}
Line Property string Line {get;set;}
LineNumber Property int LineNumber {get;set;}
Matches Property System.Text.RegularExpressions.Match[] Matches {get;set;}
Path Property string Path {get;set;}
Pattern Property string Pattern {get;set;}
And other properties, such as Pattern and Line work:
PS H:\> $c.Pattern
ab
PS H:\> $c.Line
abd 14e 568
Also, no error is generated when sending an index value to the Matches array:
PS H:\> $c.Matches[0]
PS H:\>
I am not certain how to interpret the results, nor am I certain why it is occuring.
This behavior is problematic, as there are many times I must search for strings that contain regex special characters, ()'s are very common.
Expanding on the example:
PS H:\> $c = "ab(d) 14e 568" | Select-String -Pattern "ab(d)"
PS H:\> $c.Matches
PS H:\>
$c.Matches returns nothing, and $c itself is null, due to the use of the parentheses in the regex pattern:
PS H:\> $c -eq $null
True
Using -SimpleMatch does produce a MatchInfo object, but still does not return any matches:
PS H:\> $c = "ab(d) 14e 568" | Select-String -Pattern "ab(d)" -SimpleMatch
PS H:\> $c -eq $null
False
PS H:\> $c.Matches
PS H:\>
The work-around I found (here on SO) is to use the Regex.Escape method from .NET:
(reference: Powershell select-string fails due to escape sequence)
PS H:\> $pattern = "ab(d)"
$pattern = ([regex]::Escape($pattern))
$c = "ab(d) 14e 568" | Select-String -Pattern $pattern
PS H:\> $c.Matches
Groups : {ab(d)}
Success : True
Captures : {ab(d)}
Index : 0
Length : 5
Value : ab(d)
As this workaround returns the expected matches from Select-String, I have been able to continue my scripting.
But I am curious as to why no matches are returned when using the -SimpleMatch parameter.
...
With regards,
Schwert
回答1:
From Get-Help Select-String -Parameter SimpleMatch:
-SimpleMatch [
<SwitchParameter>]Uses a simple match rather than a regular expression match. In a simple match, Select-String searches the input for the text in the Pattern parameter. It does not interpret the value of the Pattern parameter as a regular expression statement.
So, SimpleMatch simply does a substring search for $Pattern inside each string you pipe to it. It returns a MatchInfo object containing the string and relevant contextual information if present, but no Matches since a proper regex matching was never carried out against the string - it's as simple as that
来源：https://stackoverflow.com/questions/33179734/matches-not-captured-when-using-simplematch-with-select-string