Why does Select-String add empty lines?

Question

Here is a minimal repro example.

Expected result:

PS C:\> ("a", "b")
a
b
PS C:\> ("a", "b") | Select-String "b"
b
PS C:\>

Actual result:

PS C:\> ("a", "b")
a
b
PS C:\> ("a", "b") | Select-String "b"

b


PS C:\>

As you can see, the second output has one empty line before and two empty lines after the matched lines.

Why does that happen? And what can I do about it?

(Note: This is a minimal example. In my real code, I'm parsing svn status output for uncommitted files and I get the same problem of spurious newlines.)

You can pipe that out to | Select-Object -ExpandProperty Line to get rid of the newlines but I have no idea why it adds the newlines so I'll wait for someone else to answer... — Shaneis
– Shaneis, Commented Jan 2, 2018 at 10:43
That is pure formatting artifacts. You should not depend on particular format, but should use properties to get values you need. — user4003407
– user4003407, Commented Jan 2, 2018 at 11:01
@PetSerAl are you saying that Select-String does a implicit version of Format-*? :O — Shaneis
– Shaneis, Commented Jan 2, 2018 at 11:09
@Shaneis No. Default Out-Default have implicit version of Format-*. — user4003407
– user4003407, Commented Jan 2, 2018 at 11:12

vonPryz · Accepted Answer · 2018-01-02 12:14:29Z

15

The reason for weird output is that Powershell is all about objects. In this particular case, Select-String returns MatchInfo object(s). Like so,

PS C:\> $o = ("a", "b") | Select-String "b"
PS C:\> $o

b


PS C:\> $o.GetType()

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     False    MatchInfo                                System.Object

For extra confusion, explicit call to ToString() doesn't output the line breaks:

PS C:\> $o.ToString()
b
PS C:\>

For a work-around, query MatchInfo's Line property like so,

PS C:\>  ("a", "b") | Select-String "b" | % { $_.Line }
b
PS C:\>

Please see also Keith Hill's answer about similar a question.

edited Jan 2, 2018 at 12:14

answered Jan 2, 2018 at 12:07

vonPryz

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