Adding Arguments to PowerShell Alias Functions

Question

I just installed grep on PowerShell through chocolatey and using it, I could search for a string I want from any text as shown below:

However, I don't want to always have to type grep --color, hence I tried to make an alias on my $profile like this:

Function grep($a1){
  grep --color $a1
}

but then I would get an error:

So I tried:

Set-Alias grep "grep --color"

but then I get yet another error:

I can't think of anything else to make this work, hence I'd really appreciate any help.

That's because, *grep.exe* doesn't understand what you're telling it to work off since you're only passing it a value. You can use the [automatic variable of `$input`](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_automatic_variables?view=powershell-7.2#input) to pass over your pipeline input into *grep.exe*, and your argument. So, something like: `function grap ($text) { $input | grep --color $text}`. As for your alias, PowerShell is very literal when it comes to the `Set-Alias` cmdlet so you're basically telling it just be a string. — Abraham Zinala, Jan 24 '22 at 03:16
Good point, @Abraham, though in this case the infinite recursion to due to also naming the function `grep` is the primary problem. Also, `$input` must be only be used if actual pipeline input is present (`$MyInvocation.ExpectingInput`), so as to also enable calls where input is alternatively provided via _file paths_ passed as _arguments_. — mklement0, Jan 24 '22 at 03:53

mklement0 · Accepted Answer · 2022-01-24T03:45:11.790

Aliases in PowerShell are mere alternative names for other commands, so you cannot use them to include arguments to pass to these other commands.

You therefore indeed need a function, but since you're naming it the same as the external program you're wrapping, you need to disambiguate so as to avoid an infinite recursion:

function grep {
  $externalGrep = Get-Command -Type Application grep
  if ($MyInvocation.ExpectingInput) { # pipeline (stdin) input present
    # $args passes all arguments through.
    $input | & $externalGrep --color $args
  } else {
    & $externalGrep --color $args
  }
}

Note:

Use of the automatic $input variable to relay pipeline (stdin) input means that this input is collected (buffered) in full first. More effort is needed to implement a true streaming solution - see this answer for an example.

Alternatively - at least on Unix-like platforms - you can set an environment variable to control grep's coloring behavior, which may obviate the need for a function wrapper; the equivalent of the --color parameter is to set $env:GREP_COLOR='always' (the other supported values are 'never' and 'auto').

Adding Arguments to PowerShell Alias Functions

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