Create SQL Job with Invoke-Sqlcmd

Question

I'm trying to run a set of .sql files, i didn't know how to pass a common variable to all, so i've started running the statements directly in ps.  One of these creates a job but i'm running into all of the errors due to the special characters and the
variables, can someone help?
$Client = "C0212"
$Instance = "SQL03\"+$Client
$sqlscript3 = "
--NEED TO CHANGE THE LOG LOCATION BELOW
USE [msdb]
GO
/****** Object:  Job [DatabaseBackup - USER_DATABASES - FULL]    Script Date: 11/15/2013 8:40:20 AM ******/
BEGIN TRANSACTION
DECLARE @ReturnCode INT
SELECT @ReturnCode = 0
/****** Object:  JobCategory [Database Maintenance]    Script Date: 11/15/2013 8:40:20 AM ******/
IF NOT EXISTS (SELECT name FROM msdb.dbo.syscategories WHERE name=N''Database Maintenance'' AND category_class=1)
BEGIN
EXEC @ReturnCode = msdb.dbo.sp_add_category @class=N''JOB'', @type=N''LOCAL'', @name=N''Database Maintenance''
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
END
DECLARE @jobId BINARY(16)
EXEC @ReturnCode =  msdb.dbo.sp_add_job @job_name=N''DatabaseBackup - USER_DATABASES - FULL'', 
@enabled=1, 
@notify_level_eventlog=2, 
@notify_level_email=0, 
@notify_level_netsend=0, 
@notify_level_page=0, 
@delete_level=0, 
@description=N''Source: http://ola.hallengren.com'', 
@category_name=N''Database Maintenance'', 
@owner_login_name=N''sa'', @job_id = @jobId OUTPUT
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
/****** Object:  Step [DatabaseBackup - USER_DATABASES - FULL]    Script Date: 11/15/2013 8:40:20 AM ******/
EXEC @ReturnCode = msdb.dbo.sp_add_jobstep @job_id=@jobId, @step_name=N''DatabaseBackup - USER_DATABASES - FULL'', 
@step_id=1, 
@cmdexec_success_code=0, 
@on_success_action=1, 
@on_success_step_id=0, 
@on_fail_action=2, 
@on_fail_step_id=0, 
@retry_attempts=0, 
@retry_interval=0, 
@os_run_priority=0, @subsystem=N''CmdExec'', 
@command=N''sqlcmd -E -S `$(ESCAPE_SQUOTE(SRVR)) -d DBA -Q `"EXECUTE [dbo].[DatabaseBackup] @Databases = ''''USER_DATABASES'''', @Directory = N''''T:\SQLsafe Backups\SQL Native Backup'''', @BackupType = ''''FULL'''',
@Verify = ''''Y'''', @CleanupTime = 170, @CheckSum = ''''Y'''', @LogToTable = ''''Y''''`" -b'', 
--NEED TO CHANGE THE LOG LOCATION BELOW
@output_file_name=N''C:\Program Files\Microsoft SQL Server\MSSQL11.$Client\MSSQL\LOG\DatabaseBackup_`$(ESCAPE_SQUOTE(JOBID))_`$(ESCAPE_SQUOTE(STEPID))_`$(ESCAPE_SQUOTE(STRTDT))_`$(ESCAPE_SQUOTE(STRTTM)).txt'', 
@flags=0
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_update_job @job_id = @jobId, @start_step_id = 1
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_add_jobschedule @job_id=@jobId, @name=N''Saturday 4am'', 
@enabled=1, 
@freq_type=8, 
@freq_interval=64, 
@freq_subday_type=1, 
@freq_subday_interval=0, 
@freq_relative_interval=0, 
@freq_recurrence_factor=1, 
@active_start_date=20131109, 
@active_end_date=99991231, 
@active_start_time=40000, 
@active_end_time=235959, 
@schedule_uid=N''5b3c3fcf-28dc-4f4c-95ce-a624667ee378''
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_add_jobserver @job_id = @jobId, @server_name = N''(local)''
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
COMMIT TRANSACTION
GOTO EndSave
QuitWithRollback:
    IF (@@TRANCOUNT > 0) ROLLBACK TRANSACTION
EndSave:
GO"
Invoke-Sqlcmd –ServerInstance $Instance –Database msdb –Query $sqlscript3 -QueryTimeout 300

Answer 1

So, if I try this:
$Client = "C0212"
Invoke-Sqlcmd -InputFile "C:\NewInstanceScripts\PSNI -3 - Create Full Backup job for ALL User Databases.sql" -Variable $Client
and in my .sql file that line that contains the variable looks like this:
@output_file_name=N'C:\Program Files\Microsoft SQL Server\MSSQL11.`$(Client)\MSSQL\LOG\DatabaseBackup_$(ESCAPE_SQUOTE(JOBID))_$(ESCAPE_SQUOTE(STEPID))_$(ESCAPE_SQUOTE(STRTDT))_$(ESCAPE_SQUOTE(STRTTM)).txt',
I get the error: 
Invoke-Sqlcmd : The format used to define the new variable for Invoke-Sqlcmd cmdlet is invalid. Please use the 'var=value' format for defining a new variable.
If i try like this:
Set @Client = "C0212"
Invoke-Sqlcmd -InputFile "C:\NewInstanceScripts\PSNI -3 - Create Full Backup job for ALL User Databases.sql" -Variable @Client
Line in .sql file like this:
@output_file_name=N'C:\Program Files\Microsoft SQL Server\MSSQL11.@Client\MSSQL\LOG\DatabaseBackup_$(ESCAPE_SQUOTE(JOBID))_$(ESCAPE_SQUOTE(STEPID))_$(ESCAPE_SQUOTE(STRTDT))_$(ESCAPE_SQUOTE(STRTTM)).txt',
I get the error: Set-Variable : A positional parameter cannot be found that accepts argument '2'.