Using PowerShell sls (Select-String) vs grep vs findstr

Question

Could someone clarify how sls (Select-String) works compared to grep and findstr?

grep: grep files.txt

sls: sls

Answer 1

To complement AdminOfThings' helpful answer:

• In order to find strings among the lines of the for-display string representations of non-string input objects as they would print to the console you indeed have to pipe to Out-String -Stream, whereas by default, simple .ToString() stringification is applied^[1].

  • You shouldn't have to do this manually, however: Select-String should do it implicitly, as suggested in this GitHub issue.

• Curiously, when piping to external programs such as findstr.exe, PowerShell already does apply Out-String -Stream implicitly; e.g:

  • Get-Date 1/1/2019 | findstr January works (in en-based cultures), because it is implicitly the same as
    Get-Date 1/1/2019 | Out-String -Stream | findstr January
  • By contrast, Get-Date 1/1/2019 | Select-String January is the equivalent of
    (Get-Date 1/1/2019).ToString([cultureinfo]::InvariantCulture) | Select-String January, and therefore does not work, because the input evaluates to 01/01/2019 00:00:00.

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^{[1] More accurately, .psobject.ToString() is called, either as-is, or - if the object's ToString method supports an IFormatProvider-typed argument - as .psobject.ToString([cultureinfo]::InvariantCulture) so as to obtain a culture-invariant representation - see this answer for more information.}

Answer 2

When you use Out-String by default, it turns the piped input object (an array of service objects in this case) into a single string. Luckily, the -Stream switch allows each line to be output as a single string instead. Regarding case-sensitivity, Select-String supports the -CaseSensitive switch.

# For case-insensitive regex match
Get-Service | Out-String -Stream | Select-String "Sec"

# For case-sensitive regex match
Get-Service | Out-String -Stream | Select-String "Sec" -CaseSensitive

# For case-sensitive non-regex match
Get-Service | Out-String -Stream | Select-String "Sec" -CaseSensitive -SimpleMatch

In either case, Select-String uses regex (use the -SimpleMatch switch to do a string match) to pattern match against each input string and outputs the entire string that matched the pattern. So if you only pipe into it a single string with many lines, then all lines will be returned on a successful match.