diff --git a/usha.nim b/usha.nim
index 73f4847..b2ce2ac 100644
--- a/usha.nim
+++ b/usha.nim
@@ -7,28 +7,32 @@ import ushapkg/[db, logger]
 const
   programName = "usha"
   help = """
-hist: search your command-line history.
+$1: search your command-line history.
 
 Usage:
   $1 init [-v]
   $1 clean [DAYS]
-  $1 update [-v] CMD
+  $1 update [-v] CMD [-c CHECKSUM]
   $1 [DIR] [-n N] [-tvrs SEARCHSTRING]
 
 Options:
   DIR             Directory to search within.
-  CMD          Insert command into database.
-  DAYS         Number of days of history to preserve. [default: 60]
+  CMD             Insert command into database.
+  DAYS            Number of days of history to preserve. [default: 60]
   -n N            Retrieve the N most common commands. [default: 5]
   -s SEARCHSTRING Search for commands containing a string.
   -t              Order by most recently entered.
   -v              Verbose.
   -r              Recurse current directory.
+  -c CHECKSUM     Optional argument to update to prevent duplication.
 """ % programName
 
-proc filter(stopWords: HashSet[string], cmd: string): bool =
+proc filter(ignorePath, cmd: string): bool =
   ## Verify that a command is not 0-length and is not in the ignore
   ## list.
+  if not existsFile(ignorePath):
+    return true
+  let stopWords = toSeq(lines(ignorePath)).toSet
   case cmd
   of "":
     false
@@ -57,15 +61,32 @@ proc historyInit() {.raises: [].} =
     except ValueError:
       quit "Unknown failure during database initialization."
 
-proc historyUpdate(cwd, cmd: string, stopWords: HashSet[string]) {.raises: [].} =
-  if stopWords.filter(cmd):
+proc historyUpdate(args: Table[string, docopt.Value]) {.raises: [].} =
+  const
+    ignoreFile = ".$1ignore" % programName
+    genericErrorMessage = "Unknown failure during database insertion."
+
+  try:
+    let
+      cwd = getCurrentDir()
+      cmd = $args["CMD"]
+      checksum = if args["-c"]: $args["-c"] else: nil
+      ignorePath = getHomeDir() / ignoreFile
+
+    if not ignorePath.filter(cmd):
+      log "Skipping update; value in stop words: " & cmd
+    elif not checksum.isNil and not dbChecksum(checksum):
+      log "Skipping update; checksum matches: " & checksum
+    else:
+      dbInsert(cwd, cmd, checksum)
+
+  except DbError as e:
     try:
-      dbInsert(cwd, cmd)
-    except DbError as e:
-      try:
-        handleDbError(e, "Could not insert command into $1 database." % programName)
-      except ValueError:
-        quit "Unknown failure during database insertion."
+      handleDbError(e, "Could not insert command into $1 database." % programName)
+    except ValueError:
+      quit genericErrorMessage
+  except Exception, AssertionError, IOError:
+    quit genericErrorMessage
 
 proc historyClean(args: Table[string, docopt.Value]) {.raises: [] .} =
   try:
@@ -110,31 +131,23 @@ proc historySearch(args: Table[string, docopt.Value]) {.raises: [].} =
     except ValueError:
       quit "Unknown error during database search."
 
-when isMainModule:
-  var args = docopt(help)
-
+proc processArgs(args: Table[string, Value]) =
   if args["-v"]:
     setLogLevel vVerbose
 
-  discard dbOpen()
-  defer: dbClose()
-
   if args["init"]:
     historyInit()
-
   elif args["update"]:
-    var ignoreLines: HashSet[string]
-    const ignoreFile = ".ushaignore"
-
-    let
-      ignorePath = getHomeDir() / ignoreFile
-    if existsFile(ignorePath):
-      ignoreLines = toSeq(lines(ignorePath)).toSet
-
-    historyUpdate(getCurrentDir(), $args["CMD"], ignoreLines)
-
+    historyUpdate(args)
   elif args["clean"]:
     historyClean(args)
-
   else:
     historySearch(args)
+
+when isMainModule:
+  var args = docopt(help)
+
+  discard dbOpen()
+  defer: dbClose()
+
+  processArgs(args)
diff --git a/usha.nimble b/usha.nimble
index 85fd202..e03400c 100644
--- a/usha.nimble
+++ b/usha.nimble
@@ -1,6 +1,6 @@
 # Package
 
-version       = "0.1.0"
+version       = "0.2"
 author        = "Zach Smith"
 description   = "untitled shell history application"
 license       = "MIT"
diff --git a/ushapkg/db.nim b/ushapkg/db.nim
index 7974c7a..810472c 100644
--- a/ushapkg/db.nim
+++ b/ushapkg/db.nim
@@ -34,6 +34,15 @@ proc dbInit*() =
   db.exec sql"CREATE UNIQUE INDEX IF NOT EXISTS command_idx ON ? (cwd, cmd)", tableName
   db.exec sql"CREATE INDEX IF NOT EXISTS count_order_idx ON ? (count)", tableName
   db.exec sql"CREATE INDEX IF NOT EXISTS entered_order_idx ON ? (entered_on)", tableName
+  db.exec sql"""
+    CREATE TABLE IF NOT EXISTS checksum (
+        hash        VARCHAR(256)
+    )"""
+  db.exec sql"""
+    INSERT INTO checksum
+    SELECT "" WHERE NOT EXISTS (
+      SELECT 1 FROM checksum
+    )"""
 
 type SearchResponse* = object
   cmd, count, timestamp: string
@@ -142,13 +151,28 @@ proc dbSearch*(
     timestamp: if orderByTimeStamp: it[2] else: nil
   ))
 
-proc dbInsert*(cwd, cmd: string)  =
+proc dbChecksum*(checksum: string): bool =
+  log "Checking checksum against value: " & checksum
+
+  let currentValue = db.getValue sql"""
+    SELECT hash FROM checksum LIMIT 1
+  """
+  log "Current checksum value: " & currentValue
+
+  currentValue != checksum
+
+proc dbInsert*(cwd, cmd, checksum: string)  =
   db.exec sql"""
     INSERT OR REPLACE INTO ?
       (cwd, cmd, count) VALUES
       (?, ?, COALESCE(
         (SELECT count FROM ? WHERE cwd=? AND cmd=?), 0) + 1)
       """, tableName, cwd, cmd, tableName, cwd, cmd
+  if not checksum.isNil:
+    log "Updating checksum with value: " & checksum
+    db.exec sql"""
+      UPDATE checksum SET hash = ?
+    """, checksum
 
 proc dbClean*(days: string)  =
   let