I tried to create a multiline Input to practice Select-String, expecting only a single matching line to be output, like I would normaly see it in an echo -e ... | grep combination. But the following command still gives me both lines. It seems to be the newline is only interpreted on final ouptut and Select-String still gets a single line of input

Write-Output "Hi`nthere" | Select-String -Pattern "i"
#
# Hi
# there
#
#

while I would expect it to return just

Hi

I used this version of PowerShell:

Get-Host | Select-Object Version
# 5.1.19041.906

Comparing with bash I would do the following for testing commands on multiline input in bash. I usually generate multiple lines with echo -e and then grep processes the individual lines.

echo -e "Hi\nthere" | grep "i"
# Hi

I hope someone can explain what I miss here in PowerShell? This problem seems like a basic misconception to me, where I also was not sure what to Google for.

Edits

[edit 1]: problem also for line ending with carriage return

Write-Output "Hi`r`nthere" | Select-String -Pattern "i"

I saw that separating with commas works as valid multiline input. So maybe the question is how to convert from newline to actual input line separation.

Write-Output "Hi","there" | Select-String -Pattern "i"
# Hi

[edit 2]: from edit 1 I found this stackoverflow-answer, where for me it now works with

Write-Output "Hi`nthere".Split([Environment]::NewLine) | Select-String -Pattern "i"
# or
Write-Output "Hi`nthere".Split("`n") | Select-String -Pattern "i"

Still may someone please explain why this is relevant here, but not in bash?

CodePudding user response：

All the information is in the comments, but let me summarize and complement it:

PowerShell's pipeline is object-based, and Select-String operates on each input object - even if that happens to be a single multi-line string object, such as output by Write-Output "Hi`nthere"

• It is only the output from external programs that is streamed line by line.

Therefore, you must split your multi-line string into individual lines in order to match them as such.

The best idiom for that is -split '\r?\n', because it recognizes both Windows-format CRLF and Unix-format LF-only newlines :

"Hi`nthere" -split '\r?\n' | Select-String -Pattern "i"

Note:

• I've omitted Write-Output in favor of PowerShell's implicit output behavior (see the bottom section of this answer for more information).

• For more information on how -split '\r?\n' works, see this answer.

• Select-String doesn't directly output the matching lines (strings); instead it wraps them in match-information objects that provide metadata about each match. To get just the matching line (string):

  • In PowerShell (Core) 7 , add the -Raw switch.
  • In Windows PowerShell, pipe to ForEach-Object Line or wrap the entire call in (...).Line