Found this PowerShell script which scans these areas to to retrieve a specific user's access rights:


Farm Administrator's Group
Central Administration Web Application Policies
Site Collection Administrators 
Scans the all Site collections and Sub-sites with Unique Permissions
Scans all Lists and Libraries with unique permissions
Scans all Groups which has permissions on sites and Lists


After executing the script, it generates a CSV file (Tab Separated, In fact!) with details: URL, Site/List, Title, Permission Type, Permissions as in the below screenshot.

Refer: SharePoint Permission Report: Check Access Rights for a Specific User
http://www.sharepointdiary.com/2013/01/permission-report-for-specific-user.html

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

Function GetUserAccessReport($WebAppURL, $SearchUser)
{
 #Get All Site Collections of the WebApp
 $SiteCollections = Get-SPSite -WebApplication $WebAppURL -Limit All

#Write CSV- TAB Separated File) Header
"URL `t Site/List `t Title `t PermissionType `t Permissions" | out-file UserAccessReport.csv

  #Check Whether the Search Users is a Farm Administrator
  $AdminWebApp= Get-SPwebapplication -includecentraladministration | where {$_.IsAdministrationWebApplication}
    $AdminSite = Get-SPweb($AdminWebApp.Url)
   $AdminGroupName = $AdminSite.AssociatedOwnerGroup
    $FarmAdminGroup = $AdminSite.SiteGroups[$AdminGroupName]

     foreach ($user in $FarmAdminGroup.users)
      {
       if($user.LoginName -eq $SearchUser)
    {
     "$($AdminWebApp.URL) `t Farm `t $($AdminSite.Title)`t Farm Administrator `t Farm Administrator" | Out-File UserAccessReport.csv -Append
    }     
      }

 #Check Web Application Policies
 $WebApp= Get-SPWebApplication $WebAppURL

 foreach ($Policy in $WebApp.Policies)
   {
   #Check if the search users is member of the group
  if($Policy.UserName -eq $SearchUser)
     {
    #Write-Host $Policy.UserName
     $PolicyRoles=@()
     foreach($Role in $Policy.PolicyRoleBindings)
    {
     $PolicyRoles+= $Role.Name +";"
    }
    #Write-Host "Permissions: " $PolicyRoles

    "$($AdminWebApp.URL) `t Web Application `t $($AdminSite.Title)`t  Web Application Policy `t $($PolicyRoles)" | Out-File UserAccessReport.csv -Append
   }
   }

  #Loop through all site collections
   foreach($Site in $SiteCollections)
    {
   #Check Whether the Search User is a Site Collection Administrator
   foreach($SiteCollAdmin in $Site.RootWeb.SiteAdministrators)
       {
    if($SiteCollAdmin.LoginName -eq $SearchUser)
   {
    "$($Site.RootWeb.Url) `t Site `t $($Site.RootWeb.Title)`t Site Collection Administrator `t Site Collection Administrator" | Out-File UserAccessReport.csv -Append
   }     
  }

    #Loop throuh all Sub Sites
       foreach($Web in $Site.AllWebs)
       {
   if($Web.HasUniqueRoleAssignments -eq $True)
             {
          #Get all the users granted permissions to the list
             foreach($WebRoleAssignment in $Web.RoleAssignments )
                 {
                   #Is it a User Account?
      if($WebRoleAssignment.Member.userlogin)   
       {
          #Is the current user is the user we search for?
          if($WebRoleAssignment.Member.LoginName -eq $SearchUser)
         {
          #Write-Host  $SearchUser has direct permissions to site $Web.Url
          #Get the Permissions assigned to user
           $WebUserPermissions=@()
             foreach ($RoleDefinition  in $WebRoleAssignment.RoleDefinitionBindings)
             {
                             $WebUserPermissions += $RoleDefinition.Name +";"
                            }
          #write-host "with these permissions: " $WebUserPermissions
          #Send the Data to Log file
          "$($Web.Url) `t Site `t $($Web.Title)`t Direct Permission `t $($WebUserPermissions)" | Out-File UserAccessReport.csv -Append
         }
       }
     #Its a SharePoint Group, So search inside the group and check if the user is member of that group
     else 
      {
                        foreach($user in $WebRoleAssignment.member.users)
                            {
           #Check if the search users is member of the group
         if($user.LoginName -eq $SearchUser)
          {
           #Write-Host  "$SearchUser is Member of " $WebRoleAssignment.Member.Name "Group"
            #Get the Group's Permissions on site
         $WebGroupPermissions=@()
            foreach ($RoleDefinition  in $WebRoleAssignment.RoleDefinitionBindings)
            {
                           $WebGroupPermissions += $RoleDefinition.Name +";"
                           }
         #write-host "Group has these permissions: " $WebGroupPermissions

         #Send the Data to Log file
         "$($Web.Url) `t Site `t $($Web.Title)`t Member of $($WebRoleAssignment.Member.Name) Group `t $($WebGroupPermissions)" | Out-File UserAccessReport.csv -Append
        }
       }
      }
                    }
    }

    #********  Check Lists with Unique Permissions ********/
              foreach($List in $Web.lists)
              {
                  if($List.HasUniqueRoleAssignments -eq $True -and ($List.Hidden -eq $false))
                  {
                     #Get all the users granted permissions to the list
                foreach($ListRoleAssignment in $List.RoleAssignments )
                    {
                      #Is it a User Account?
         if($ListRoleAssignment.Member.userlogin)   
          {
             #Is the current user is the user we search for?
             if($ListRoleAssignment.Member.LoginName -eq $SearchUser)
            {
             #Write-Host  $SearchUser has direct permissions to List ($List.ParentWeb.Url)/($List.RootFolder.Url)
             #Get the Permissions assigned to user
              $ListUserPermissions=@()
                foreach ($RoleDefinition  in $ListRoleAssignment.RoleDefinitionBindings)
                {
                                $ListUserPermissions += $RoleDefinition.Name +";"
                               }
             #write-host "with these permissions: " $ListUserPermissions

             #Send the Data to Log file
             "$($List.ParentWeb.Url)/$($List.RootFolder.Url) `t List `t $($List.Title)`t Direct Permissions `t $($ListUserPermissions)" | Out-File UserAccessReport.csv -Append
            }
          }
          #Its a SharePoint Group, So search inside the group and check if the user is member of that group
         else 
          {
                             foreach($user in $ListRoleAssignment.member.users)
                                 {
              if($user.LoginName -eq $SearchUser)
               {
                #Write-Host  "$SearchUser is Member of " $ListRoleAssignment.Member.Name "Group"
                 #Get the Group's Permissions on site
              $ListGroupPermissions=@()
                 foreach ($RoleDefinition  in $ListRoleAssignment.RoleDefinitionBindings)
                 {
                                $ListGroupPermissions += $RoleDefinition.Name +";"
                                }
              #write-host "Group has these permissions: " $ListGroupPermissions

              #Send the Data to Log file
              "$($Web.Url) `t Site `t $($List.Title)`t Member of $($ListRoleAssignment.Member.Name) Group `t $($ListGroupPermissions)" | Out-File UserAccessReport.csv -Append
             }
            }
         }
                       }
                }
              }
    }
   }

  }

#Call the function to Check User Access
GetUserAccessReport "http://sharepoint.crescent.com" "Global\Salaudeen"


Read more: http://www.sharepointdiary.com/2013/01/permission-report-for-specific-user.html#ixzz2macjy36a

Powershell script to find permissions for a specific user
When i run my script like so: 

C:\>perl script.pl -f file

It works fine. But, if I just do:

C:\>script.pl -f file

then I don't get any errors but getopts doesn't assign anything to $opt_f

This works just fine on perl 5.8 Windows XP, but it doesn't work on perl 5.12 on Windows 7.
There aren't any other versions of perl installed (its a new OS build).

Code:

use Getopt::Std;
our ($opt_f);
getopts('f:');
print "input file is: $opt_f \n";
print "$0\n


Run with:

C:\&gt; perl get.pl -f sadf
input file is: sadf
get.pl


Run without:

C:\&gt;get.pl -f sadf
input file is:


Nothing!

EDIT:  fixed and this question was a repeat...
http://stackoverflow.com/questions/1695188/how-do-i-make-perl-scripts-recognize-parameters-in-the-win32-cmd-console

The OP of that post figured it out.
I had to do the same but also recreate the assoc in the gui (in addition to in the reg and on the command line with ftype.)  
