dotnet ef scaffold Unrecognized option '-t firstTable -t secondTable' - pass arguments stored in a string

Question

I have a .ps1 file that I run from PowerShell, the code is as follows:

$strTables = ""
$tables | ForEach-Object{            
    $strTables += "-t $_ "  
}
# $strTables = -t fisrtTable -t secondTable
dotnet ef dbcontext scaffold $strConn Npgsql.EntityFrameworkCore.PostgreSQL --context MyModel $strTables -v -f

If I put the variable $strTable in the command it does not recognise the -t parameter (but the variable $strConn does work)

Unrecognized option '-t fisrtTable -t secondTable'

If I write the tables without the variable, it works.

dotnet ef dbcontext scaffold $strConn Npgsql.EntityFrameworkCore.PostgreSQL --context MyModel -t firstTable -t secondTable -v -f

I have too many tables to do this manually. Do you know how I can concatenate variable $strTables with the dotnet command?

Thanks in advance

This has nothing to with C#, .NET or Entity Framework, it's entirely PowerShell. You need to use Invoke-Expression if you want to execute a command line from a string. — DavidG
– DavidG, Commented Aug 2, 2022 at 13:31
@DavidG, while Invoke-Expression technically works, it is generally best avoided, as there are usually superior - and safer - alternatives. Indeed, constructing the arguments as individual elements of an array is the preferable solution here. — mklement0
– mklement0, Commented Dec 2, 2022 at 21:07

mklement0 · Accepted Answer · 2025-10-26 20:10:47Z

If you construct a string such as -t foo and pass it via a variable to an external program, it is passed as a single, double-quoted argument (that is, donet will literally see "-t foo" on its command line) - and therefore won't be recognized as parameter name-value combination.

You must pass -t and foo separately, as elements of an array instead.
When you use an array as an argument for an external program, PowerShell passes the array elements as individual, space-separated arguments:

# Create an array such as '-t', 'foo', '-t', 'bar', ...
$tableArgs = 
  $tables | ForEach-Object {            
    '-t', "$_"  
  }

# Note the use of $tableArgs as-is, which causes PowerShell to pass
# e.g. ... -t foo -t bar ... behind the scenes.
dotnet ef dbcontext scaffold $strConn Npgsql.EntityFrameworkCore.PostgreSQL --context MyModel $tableArgs -v -f

To provide a simpler example: The equivalent of foo -s -o "bar baz" file1 is:

$a = @('-s', '-o', 'bar baz', 'file1') # construct the array of arguments
foo $a  # or: foo @a

As the first code snippet implies, you're free to mix explicitly specified arguments with those provided via an array.

As an aside:

If the array containing the argument is stored in a variable, you may alternatively use splatting, i.e yo may pass @tableArgs (@ instead of $). However, given that with external programs and arrays this is the same as passing an array (variable) directly, there is no strict advantage in doing so, though you may prefer the @ sigil for conceptual clarity.
- However, (explicit) splatting with @ is necessary in order to pass programmatically constructed arguments to PowerShell commands, where it is more commonly based on a hashtable whose keys identify the target parameters, which enables passing named arguments.
On a general note: Whether or not you pass arguments literally, via variables, or by way of an array, PowerShell's passing of arguments with embedded " chars. as well as passing the empty string as an argument to external programs is broken in Windows PowerShell and PowerShell (Core) 7 up to v7.2.x, and requires workarounds - see this answer for details.

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