Powershell: Select-String -SimpleMatch should be mutually exclusive with -AllMatches, but the combination is currently accepted and quietly ignored

[mklement0]

When you specify -SimpleMatch, the output objects' .Matches property isn't populated at all - the only information about the input string's _content_ is the .Line property.

Since all matches per input object would only be available via .Matches, specifying -AllMatches in combination with -SimpleMatch is pointless and _should be prevented_.

My guess is that the -rare - instances of this pointless combination in existing code stem from a misconception of what -AllMatches does; users may mistakenly think that -AllMatches is necessary to find all matches in a _file_ (which happens by default), whereas in reality it is used to find all matches on each _line_.

As an aside: The alternative would be to also capture literal matches with -SimpleMatch (both one by default, and all with -AllMatches), but (a) that would be a nontrivial enhancement and (b) is of less interest than with regexes; that said, it would still be of interest in two respects:

• if you match literally, but case-INsensitively with -SimpleMatch, and are interested in the specific case variation of the matching parts of the input line.

• Even with literal matching you may be interested in _how many_ matches occurred per line.

Steps to reproduce

# Without `-SimpleMatch`: OK, because .Matches is populated
('foo,foo' | Select-String -Pattern foo -AllMatches).Matches.Count | Should -Be 2

# With -SimpleMatch:
# The matching parts of the input lines aren't captured at all, so -AllMatches makes no sense.
# An error should be thrown, but currently isn't:
{ 'foo,foo' | Select-String -SimpleMatch foo -AllMatches } | Should -Throw

Expected behavior

Both tests should pass.

Actual behavior

The 2nd test fails:

 Expected an exception, to be thrown, but no exception was thrown

Environment data

PowerShell Core 7.0.0-preview.5

[iSazonov]

I prepared the fix but it is a breaking change if now we will throw in the case.

[mklement0]

Thanks, @iSazonov.

Good point - since specifying the inapplicable switch has currently no effect whatsoever, current code that uses it - meaninglessly - could conceivably break.

My _hunch_ is that we're talking about a Bucket 3: Unlikely Grey Area](https://github.com/PowerShell/PowerShell/blob/master/docs/dev-process/breaking-change-contract.md#bucket-3-unlikely-grey-area) change, however, given that -SimpleMatch itself appears not to be used all that frequently.

Searching for https://github.com/search?q=select-string++simplematch+allmatches&type=Code
brings up only 79 code matches (most of them duplicates, and most of them PowerShell documentation / source code), but I did find 4 instances of combining -AllMatches with -SimpleMatch, across 3 repos:

• https://github.com/AditiTechnologies/Brewmaster.ElasticSearch

  • https://github.com/AditiTechnologies/Brewmaster.ElasticSearch/blob/46376ba98ad458a3ddb022287046d5073d589377/Brewmaster%20Elastic%20Search%20Template.linq
  • https://github.com/AditiTechnologies/Brewmaster.ElasticSearch/blob/46376ba98ad458a3ddb022287046d5073d589377/Template.json

• https://github.com/bmmcclint/ps_scripts

  • https://github.com/bmmcclint/ps_scripts/blob/1088d614e4122d4a9de5343531d45785e15ac14d/slack_themer.ps1
  • Repo read-me states that is a WIP.

• https://github.com/miwaniza/Autodesk_Vault_Programmers_Cookbook

  • Repo is associated with a book whose linked page no longer seems to exists (don't follow the links).
  • https://github.com/miwaniza/Autodesk_Vault_Programmers_Cookbook/blob/f07962969e92ce07573adf969b17a4826c9c12c7/test/licensed%20users.ps1

Given this, my vote is to make the change, not least because users should know that the combination doesn't make sense, so that the code doesn't end up not doing what they think it does.

GitHub

PowerShell/PowerShell

PowerShell for every system! Contribute to PowerShell/PowerShell development by creating an account on GitHub.

GitHub

AditiTechnologies/Brewmaster.ElasticSearch

Brewmaster template for ElasticSearch on Windows Azure IaaS - AditiTechnologies/Brewmaster.ElasticSearch

GitHub

AditiTechnologies/Brewmaster.ElasticSearch

Brewmaster template for ElasticSearch on Windows Azure IaaS - AditiTechnologies/Brewmaster.ElasticSearch

GitHub

AditiTechnologies/Brewmaster.ElasticSearch

Brewmaster template for ElasticSearch on Windows Azure IaaS - AditiTechnologies/Brewmaster.ElasticSearch

GitHub

bmmcclint/ps_scripts

Various PowerShell Scripts . Contribute to bmmcclint/ps_scripts development by creating an account on GitHub.

GitHub

bmmcclint/ps_scripts

Various PowerShell Scripts . Contribute to bmmcclint/ps_scripts development by creating an account on GitHub.

GitHub

miwaniza/Autodesk_Vault_Programmers_Cookbook

Code examples for Autodesk Vault Programmers Cookbook on http://zippybytes.blogspot.com - miwaniza/Autodesk_Vault_Programmers_Cookbook

GitHub

miwaniza/Autodesk_Vault_Programmers_Cookbook

Code examples for Autodesk Vault Programmers Cookbook on http://zippybytes.blogspot.com - miwaniza/Autodesk_Vault_Programmers_Cookbook

[vexx32]

Seems like a fairly sound analysis to me. If users are using switches in tandem that simply don't work that way, they should be notified of that fact.