How do I return only the matching regular expression when I select-string(grep) in PowerShell?

Question

I am trying to find a pattern in files. When I get a match using Select-String I do not want the entire line, I just want the part that matched.

Is there a parameter I can use to do this?

For example:

If I did

select-string .-.-.

and the file contained a line with:

abc 1-2-3 abc

I'd like to get a result of just 1-2-3 instead of the entire line getting returned.

I would like to know the Powershell equivalent of a grep -o

If part of your regexp is used to filter the lines you print, but you don't want to print that part, you can use lookahead and lookbehind groups (same as `grep -ohP`). Suppose you want to get the number in `keep 123 good` but not in `drop 456 nogood` then you can use `(Select-String '(?>=keep )123(?= good)' myfile.txt).Matches.Value`, result: `123` — Andrew Spencer, Dec 06 '21 at 11:11

score 43 · Answer 1 · answered May 01 '09 at 18:06

43

Or just:

Select-String .-.-. .\test.txt -All | Select Matches

answered May 01 '09 at 18:06

Keith Hill

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To add some additional information: `Select[-Object] Matches` outputs _custom objects_ with a `.Matches` property copied from `Select-String`'s `[Microsoft.PowerShell.Commands.MatchInfo]`-typed output objects. If you want to output the actual _text_ captured by the regex, use `ForEach-Object { $_.Matches[0].Value }` instead, assuming there's only 1 match per line. If there are multiple - which there could be due to `-All[Matches]`, the `grep -o` equivalent - you can use `ForEach-Object { $_.Matches.Value }` in PSv3+; in PSv2 you'd have to enumerate the `$_.Matches` collection explicitly. – mklement0 May 26 '18 at 07:22
11

`echo "abcd" | Select-String -Pattern '(ab)' | Select Matches` returns {0} – john k Oct 12 '21 at 19:56
Yeah this just returns stuff like `{0, 0, 0, 0, ...}` and not the actual matched values.... – Douglas Gaskell Nov 11 '22 at 18:47
1

and `ForEach-Object { $_.Matches.Value }` returns one blank line per match... – Douglas Gaskell Nov 11 '22 at 18:48

score 36 · Accepted Answer · answered Apr 30 '09 at 00:25

David's on the right path. [regex] is a type accelerator for System.Text.RegularExpressions.Regex

[regex]$regex = '.-.-.'
$regex.Matches('abc 1-2-3 abc') | foreach-object {$_.Value}
$regex.Matches('abc 1-2-3 abc 4-5-6') | foreach-object {$_.Value}

You could wrap that in a function if that is too verbose.

stej · Answer 3 · 2009-04-30T07:07:29.080

31

I tried other approach: Select-String returns property Matches that can be used. To get all the matches, you have to specify -AllMatches. Otherwise it returns only the first one.

My test file content:

test test1 alk atest2 asdflkj alj test3 test
test test3 test4
test2

The script:

select-string -Path c:\temp\select-string1.txt -Pattern 'test\d' -AllMatches | % { $_.Matches } | % { $_.Value }

returns

test1 #from line 1
test2 #from line 1
test3 #from line 1
test3 #from line 2
test4 #from line 2
test2 #from line 3

Select-String at technet.microsoft.com

edited Apr 30 '09 at 07:07

answered Apr 30 '09 at 06:52

stej

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I couldn't get this one working, i only have access to PS 1.0 and it doesn't look like -AllMatches is recognized in 1.0 at least. Thanks anyways! – Skyler Apr 30 '09 at 15:28
Hmm, I work with v2, ctp3. I have no possibility to try to solve that on v1, so sorry.. – stej Apr 30 '09 at 20:41
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Support for matches was added in v2, in addition to context. – JasonMArcher May 01 '09 at 02:05

score 16 · Answer 4 · edited Sep 08 '13 at 19:22

In the spirit of teach a man to fish ...

What you want to do is pipe the output of your select-string command into Get-member, so you can see what properties the objects have. Once you do that, you'll see "Matches" and you can select just that by piping your output to | **Select-Object** Matches.

My suggestion is to use something like: select linenumber, filename, matches

For example: on stej's sample:

sls .\test.txt -patt 'test\d' -All |select lineNumber,fileName,matches |ft -auto

LineNumber Filename Matches
---------- -------- -------
         1 test.txt {test1, test2, test3}
         2 test.txt {test3, test4}
         3 test.txt {test2}

score 13 · Answer 5 · edited Apr 08 '19 at 12:54

13

None of the above answers worked for me. The below did.

Get-Content -Path $pathToFile | Select-String -Pattern "'test\d'" | foreach {$_.Matches.Value}

Get-Content -Path $pathToFile | # Get-Content will divide into single lines for us

Select-String -Pattern "'test\d'" | # Define the Regex

foreach {$_.Matches.Value} # only return the value of the Object's Matches field. (This allows for multiple result matches.)

edited Apr 08 '19 at 12:54

not2qubit

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answered Jun 25 '18 at 19:36

7r4c0r

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powerShell 7.1 requires `-AllMatches` to be used with `select-string` to return all matches, like `"test1 test2 test3" | Select-String -Pattern "test\d" -AllMatches | foreach {$_.Matches.Value}`. Only first match is returned by `select-string` otherwise – oleksa Dec 04 '20 at 10:38
Working fine without `-All` on PWSH 7.2.2, @oleksa. – André Levy Apr 08 '22 at 00:02

Carl Walsh · Answer 6 · 2021-10-27T23:05:29.590

11

Instead of piping to % or select you can use simpler .prop Member Enumeration syntax, which magically works on multiple elements:

(Select-String .-.-. .\test.txt -All).Matches.Value

or less parentheses:

$m = Select-String .-.-. .\test.txt -All
$m.Matches.Value

edited Oct 27 '21 at 23:05

answered Jun 23 '21 at 18:00

Carl Walsh

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This saves so much pain and typing! – Chris F Carroll May 27 '22 at 22:19

score 5 · Answer 7 · answered May 11 '21 at 17:32

5

If you don't want to use ForEach operator, you can only use pipes and Select -Expand

For example, to get only the path after C:\, you could use :

Get-ChildItem | Select-String -Pattern "(C:\\)(.*)" | Select -Expand Matches | Select -Expand Groups | Where Name -eq 2 | Select -Expand Value

Where Name -eq 2 only selects the second match of the regex pattern specified.

answered May 11 '21 at 17:32

Adrien Constant

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for picking out the matched string when also using lookahead/lookbehind this is the approach that worked for me. `cat myfile | select-string "(?<=before).+(?=after)" | Select -Expand Matches | Select -ExpandProperty Value` – Chris F Carroll Sep 22 '21 at 15:18

score 2 · Answer 8 · answered Apr 29 '09 at 23:42

2

You can use the System.Text.RegularExpressions namespace:

http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex.aspx

answered Apr 29 '09 at 23:42

David McEwing

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That's not a solution for PowerShell though as asked for by the OP, is it? – aproximation Mar 19 '21 at 20:41

How do I return only the matching regular expression when I select-string(grep) in PowerShell?

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