Regex Guide: Getting a specific value from a text file using powershell/cmd

Question

Im using powershell or cmd to open a text file and get a specific value or text inside.

Currently the output looks like this inside the text file:

Upload Hello.zip: 0 of 933 bytes complete

Upload Hello.zip: 933 of 933 bytes complete
{
  "scanId" : 11260434,
  "scanType" : "Static",
  "analysisStatusType" : "Pending",
  "applicationName" : "Test Application Jenkins",
  "releaseName" : "Release 4",
  "microserviceName" : "",
  "__action__" : "STARTED"
}

However, I only would like to get the value from the scan ID.

This is the command I use:

Select-String -Path C:\Folder\scanjson.txt ':\s*(?<digits>[0-9]+)'

But It would return the output like this:

C:\Folder\scanjson.txt:2:Upload Hello.zip: 0 of 933 bytes complete
C:\Folder\scanjson.txt:4:Upload Hello.zip: 933 of 933 bytes complete
C:\Folder\scanjson.txt:6:  "scanId" : 11260434,

Try "scanId"\s*:\s*(?<digits>[0-9]+)?

Aicody
– Aicody

2024-06-25 18:42:31 +00:00
Commented Jun 25, 2024 at 18:42 — Aicody
– Aicody, Commented Jun 25, 2024 at 18:42

mklement0 · Accepted Answer · 2024-06-25 19:32:27Z

5

Since your text file is mostly JSON, it is better and more robust to remove the non-JSON preamble and use ConvertFrom-Json to parse the JSON into an object whose properties you can access to get the desired information:

# -> 11260434, i.e. a *number*, due to from-JSON parsing.
(
  (Get-Content -Raw C:\Folder\scanjson.txt) -replace '(?s)^.+(?=\{)' |
    ConvertFrom-Json
).scanId

Get-Content -Raw reads the file as a whole into a single, multiline string.
-replace '(?s)^.+(?=\{)' removes everything up to, but excluding, the first { character; the components of the regex are as follows:
- (?s) is an inline option that makes . match newline characters too.
- ^ matches at the start of the string.
- .+ matches any nonempty (+) run of characters (.); if your input file doesn't always have a preamble, use .* instead.
- (?=\{) is a lookahead assertion that matches a { character without including it in the match.
- By not specifying a substitution expression, the match is replaced with the empty string, i.e. effectively removed.
The resulting string is valid JSON that ConvertFrom-Json parses into [pscustomobject] instances, whose properties, such as .scanId, you can access.
- Note that, unlike the strictly text-based regex-parsing, JSON supports a few data types, causing an unquoted token such as 11260434 to be parsed as a number.
- An integer - such as in the case at hand - is parsed as type [int] (System.Int32) in Windows PowerShell vs. as [long] (System.Int64) in PowerShell (Core) 7.

As for what you tried:

Your regex was too permissive; use
"scanId"\s*:\s*(?<digits>[0-9]+) instead;^[1] i.e.:

# -> '11260434', i.e. a *string*, due to regex parsing.
(
  Select-String -List -Path C:\Folder\scanjson.txt '"scanId"\s*:\s*(?<digits>[0-9]+)'
).Matches[0].Groups['digits'].Value

Note the need to drill down into the Select-String output object, which is of type [Microsoft.PowerShell.Commands.MatchInfo], to get the capture-group value of interest.

-List ensures that matching stops after the first match.

Note: In cases where you expect multiple matches, you'd omit -List and pipe to a ForEach-Object call instead of using direct property access on the result (as shown above):
```
Select-String -Path C:\Folder\scanjson.txt '"scanId"\s*:\s*(?<digits>[0-9]+)'| 
  ForEach-Object { $_.Matches[0].Groups['digits'].Value }
```

Due to using regex-based parsing, the result is a string, simply cast the entire expression to, e.g. [int] to get a number.

^{[1] For an explanation of the regex and the option to experiment with it, see this regex101.com page. Note that regex101.com's .NET support is limited to C#, which may require tweaks to PowerShell regexes, such as not using '...' and escaping " chars. as ""; see this answer for guidance.}

edited Jun 25, 2024 at 19:32

answered Jun 25, 2024 at 18:42

mklement0

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6 Comments

George Over a year ago

Thanks! The main comment/answer worked for me. Aso for the one I tried, I was testing it on this website: regex101.com/r/IgaNue/1

mklement0 Over a year ago

Glad to hear it, @George; the Select-String solution should work too, though it returns a string (that you can easily cast to [int]). By contrast, the ConvertFrom-Json solution returns a number (of type [int] in Windows PowerShell vs. [long] in PowerShell (Core) 7)

George Over a year ago

I was using this before:

Select-String -Path C:\Folder\scanjson.txt '"scanId":\s*(?<digits>[0-9]+)' -List | ForEach-Object { $_.Matches[0].Groups['digits'].Value }

mklement0 Over a year ago

@George: That works in principle, but the regex is broken; this works:

Select-String -Path C:\Folder\scanjson.txt '"scanId"\s*:\s*(?<digits>[0-9]+)' -List | ForEach-Object { $_.Matches[0].Groups['digits'].Value }

. Since only one result is expected, my solution makes do without a ForEach-Object call.

George Over a year ago

My bad, I can confirm that the Select-String method is also now working. I could also try this command directly without having to save the data into a text file. thanks again!

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