Rename a set of files in Power Shell

Question

Hello Scripting Guys,
I am trying to rename a group of files in a given directory.  The files all start with a number and a dash (such as "1 - " or "24 - ") when I first get them. Sometimes there are files that do not start with a number or a dash in
the same directory, but I don't want to bother with those.  Of the files that do have a number and a dash, they should all be .SQL text files (have a .SQL extension).  
I want to loop through all files that meet these criteria and then rename them to the same name, but without the number and the dash.  For example a file may have a name like "1 - cust_sp_Get_Last_Order.sql"  I want to just rename this
to "cust_sp_Get_last_order.sql" and be done with it.  
I would be done by now in VBScrpt, but I am trying to learn the bloody PowerShell and it is driving me crazy.
Here is what I came up with, but it chokes on the substring piece.  If I test the substring bit by itself with variables it seems to work fine.  it just does not work in this script.  Please help.
$depfiles = gci c:\Temp -filter *.txt              
$depfiles | %{ [int]$dash_pos = $_.name.indexof("-"); 
               [int]$start = $dash_pos+2;
               [int]$dot = $_.name.indexof(".");
               [int]$end = $dot+3;
               $start; $dot; $end;
               [string]$nameonly = $_.name;
               $new_name = $nameonly.substring($start, $end);
               write "Name:" $nameonly; write "New Name:" $new_name
And this is what I get in return....
Exception calling "Substring" with "2" argument(s): "Index and length must refer to a location within 
the string.
Parameter name: length"
At C:\Users\Tom\Desktop\3rd try.ps1:9 char:47
+                $new_name = $nameonly.substring <<<< ($start, $end);
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : DotNetMethodException
Thank you.

Answer 1

Thank you both very much.
This was very helpful. The problem was I was passing the wrong value to Substring's second parameter.  The value was too high.  The value should be calucated as Brian noted: $length = $_.name.Length - $Start is correct.  I was counting spaces
from start of the string and not after the dash.
I had put "*.txt" to test it out on some test files but forgot to change it back.
Here's a semi-working version.   
$destination = "c:\deployed\"
$depfiles = gci c:\Temp -filter *.sql
cd c:\temp
$depfiles | %{ [string]$nameonly = $_.name;
               [int]$dash_pos = $_.name.indexof("-"); 
               [int]$start = $dash_pos+2;
               [int]$end = $nameonly.length;
               $end = $end-$start;
               $new_name = $nameonly.substring($start, $end);
               write ""; 
               write "";
               if ($dash_pos -gt 0) {
                    write "Name:" $nameonly; write "New Name:" ($destination + $new_name);
                    rename-item -Path $_.fullname -NewName ($destingation + $new_name);    
The rename-item cmdlet is only renaming them in the current directory, and not moving them to the deployed folder, but I need to play with it some more.  
The variables all look right however.  Any ideas?
Output:
Name:
100 - some data.sql
New Name:
c:\deployed\some data.sql
Name:
2 - big data.sql
New Name:
c:\deployed\big data.sql
Name:
99 - this is a test.sql
New Name:
c:\deployed\this is a test.sql