Fixed version of getSplitKeysForChunks

Mongo.getSplitKeysForChunks

DBCollection.prototype.getSplitKeysForChunks = function ( keyPattern, chunkSize ){

   var stats = this.stats()

   if( ! stats.sharded ){
       print( "Collection " + this + " is not sharded." )
       return
   }

   var config = this.getMongo().getDB("config")

   if( ! chunkSize ){
       chunkSize = config.settings.findOne({ _id : "chunksize" }).value
       print( "Chunk size not set, using default of " + chunkSize + "MB" )
   }
   else{
       print( "Using chunk size of " + chunkSize + "MB" )
   }

   var shardDocs = config.shards.find().toArray()

   var allSplitPoints = {}
   var numSplits = 0

   for( var i = 0; i < shardDocs.length; i++ ){

       var shardDoc = shardDocs[i]
       var shard = shardDoc._id
       var host = shardDoc.host
       var sconn = new Mongo( host )

       var chunks = config.chunks.find({ _id : sh._collRE( this ), shard : shard }).toArray()

       print( "\nGetting split points for chunks on shard " + shard + " at " + host )

       var splitPoints = []

       for( var j = 0; j < chunks.length; j++ ){
           var chunk = chunks[j]
           var result = sconn.getDB("admin").runCommand({ splitVector : this + "", min : chunk.min, max : chunk.max, maxChunkSize : chunkSize, keyPattern:keyPattern })
           if( ! result.ok ){
               print( " Had trouble getting split keys for chunk " + sh._pchunk( chunk ) + " :\n" )
               printjson( result )
           }
           else{
               splitPoints = splitPoints.concat( result.splitKeys )

               if( result.splitKeys.length > 0 )
                   print( " Added " + result.splitKeys.length + " split points for chunk " + sh._pchunk( chunk ) )
           }
       }

       print( "Total splits for shard " + shard + " : " + splitPoints.length )

       numSplits += splitPoints.length
       allSplitPoints[ shard ] = splitPoints

   }
   var migration = config.changelog.find({ what : /^move.*/ }).sort({ time : -1 }).limit( 1 ).toArray()
   if( migration.length == 0 )
       print( "\nNo migrations found in changelog." )
   else {
       migration = migration[0]
       print( "\nMost recent migration activity was on " + migration.ns + " at " + migration.time )
   }
   var admin = this.getMongo().getDB("admin")
   var coll = this
   var splitFunction = function(){

       print( "Turning off balancer..." )
       config.settings.update({ _id : "balancer" }, { $set : { stopped : true } }, true )
       print( "Sleeping for 30s to allow balancers to detect change.  To be extra safe, check config.changelog" +
              " for recent migrations." )
       sleep( 30000 )

       for( shard in allSplitPoints ){
           for( var i = 0; i < allSplitPoints[ shard ].length; i++ ){
               var splitKey = allSplitPoints[ shard ][i]
               print( "Splitting at " + tojson( splitKey ) )
               printjson( admin.runCommand({ split : coll + "", middle : splitKey }) )
           }
       }

       print( "Turning the balancer back on." )
       config.settings.update({ _id : "balancer" }, { $set : { stopped : false } } )
       sleep( 1 )
   }

   splitFunction.getSplitPoints = function(){ return allSplitPoints; }

   print( "\nGenerated " + numSplits + " split keys, run output function to perform splits.\n" +
          " ex : \n" +
          "  > var splitter = <collection>.getSplitKeysForChunks()\n" +
          "  > splitter() // Execute splits on cluster !\n" )

   return splitFunction

}
splitter = db['COLLECTION_NAME'].getSplitKeysForChunks({_id:1})
splitter();

The version in mongo shell (2.4.9) seems to be broken (it doesn't pass keyPattern into splitVector, which is a mandatory field). Otherwise it seems to work fine.