PowerShell code returning more values than expected

Question

Good evening. Stack Overflow and Powershell novice here.

The below piece of code in Powershell is returning more values than I wanted. For example, it is capturing variables in a JSON file that match PPVCOUNT but also variables named with characters before and after the PPVCount string. Example:

PPVCountAtInception

OperatorCountGreaterThanPPVCountIndicator

GOAL: My goal is to have the code only return the variable PPVCount. I also want to keep the columns: Pattern, LineNumber, Line. Forgive me for my lack of knowledge and thank you in advance

$file = 'C:\\Users\\B187515\\Downloads\\j.json'
$PPVCount="PPVCount"

Get-Content $file | Select-String -Pattern $PPVCount -Context 1| Select-Object Pattern,LineNumber, Line -ExpandProperty Context -First 18 | Format-Table | Out-file -FilePath 'C:\\Users\\B187515\\Downloads\\test.csv' -Append

Expected results:

My goal is to have the code only return the variable "PPVCount" in the CSV file. I also want to keep the columns: Pattern, LineNumber, Line

Actual results There are multiple variables returning contain "PPVCount" somewhere in the variable name. See screenshot of CSV enter image description here

-Pattern uses regex. To get only line that start with PPVCount use "^PPVCount" or only contain use "^PPVCount$" — jdweng
– jdweng, Commented Aug 1, 2024 at 9:35
As an aside: while benign in file paths, there's no reason to use \\ instead of \ in PowerShell. \ is not the escape char. in PowerShell, ` is. — mklement0
– mklement0, Commented Aug 1, 2024 at 10:42

mklement0 · Accepted Answer · 2024-08-01 11:09:46Z

1

Building on the helpful comments:

# Note: Just use '\' - no need for '\\'
$file = 'C:\Users\B187515\\Downloads\j.json'

# Enclose the property name to search for in embedded "..."
$searchRegex ='"PPVCount"'

# Pass $file (the file to search through) directly to Select-String, 
# and use Export-Csv to export the results to a CSV file.
Select-String -LiteralPath $file -Pattern $searchRegex -Context 1 | 
  Select-Object Pattern, LineNumber, Line -ExpandProperty Context -First 18 | 
  Export-Csv -LiteralPath 'C:\Users\B187515\Downloads\test.csv'

Your intent is to look for string PPVCount as a separate word; since you seem to be looking for this string as a JSON property name, you can assume that it is enclosed in embedded "..." and can therefore make it part of the search string.
- Since this amounts to a literal search, you can add the -SimpleMatch switch, which likely improves performance.
- Generally, to look for a token consisting only of letters, numbers, or _ as a separate word, you can use word-boundary assertions aka anchor (which is a regex feature and therefore requires you not to use -SimpleMatch), so the alternative in your case would be to use $searchRegex ='\bPPVCount\b'
Since your intent is to create a CSV file, use Export-Csv to create it.
- As for what you used: Both Format-Table and Out-File create representations of data for the human observer, which is why you should never use them to print data for programmatic processing - see this answer for more information.
- Character-encoding caveat: In Windows PowerShell (versions up to v5.1), Export-Csv inexplicably defaults to ASCII(!) encoding; whereas in PowerShell (Core) 7 it is commendably BOM-less UTF-8. Use an -Encoding argument as needed, but note that -Encoding utf8 invariably creates a UTF-8 file with a BOM in Windows PowerShell.
A couple of asides:
- While benign in file paths, there's no reason to use \\ instead of \ in PowerShell. \ is not the escape char. in PowerShell, ` is - see the about_Special_Characters help topic.
- The above passes the path of the file to search through directly to Select-String, via its -LiteralPath parameter. This is much more efficient than piping the lines of the file one by one to it via Get-Content, and is required if you want to see line numbers alongside the matching lines in the default display output.

answered Aug 1, 2024 at 11:09

mklement0

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4 Comments

BigSmooth82 Over a year ago

thank you all for your responses. I used $searchRegex ='"PPVCount"' , removed the \\, but I kept the Format-Table and Out-File because I am visually verifying the results.

BigSmooth82 Over a year ago

Hi @mklement0 Sometimes the output in the csv file isn't showing enough characters in that string. Is there a way to make the string longer? For example, if you look at the image I posted in the original post, I have a PostContext value like "Boolvalue":true. But sometimes my output in the CSV gets cut short and reads "boolVal" and I can't tell if the value it true of false. I only want to modify the existing code and not re-do everything I coded. Does that make sense? Thank you in advance

mklement0 Over a year ago

@BigSmooth, Format-Table can result in truncation of values, which is one of the reasons combining Select-Object and Export-Csv is preferable. If you want Format-Table to assume a certain line width that is big enough to show all values without truncation, you can pass a -Width argument to Out-File.

BigSmooth82 Over a year ago

Thank you @mklement0 stackoverflow.com/users/45375/mklement0 I also posted a new issue in a separate through. This is helpful. Can you please assist there as well? stackoverflow.com/questions/78836394/…

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