diff --git a/ssh_tools/multicopy.sh b/ssh_tools/multicopy.sh
index dca19cc..c7179f9 100755
--- a/ssh_tools/multicopy.sh
+++ b/ssh_tools/multicopy.sh
@@ -1,6 +1,6 @@
 #!/bin/sh
 #
-# multicopy.sh, Copyright © 2013 Matteo Cypriani <mcy@lm7.fr>
+# multicopy.sh, Copyright © 2013, 2019 Matteo Cypriani <mcy@lm7.fr>
 # (Formerly named cluster-deploy.sh)
 #
 # This program is free software. It comes without any warranty, to
@@ -12,6 +12,15 @@
 # Deploy files on a number of remote hosts using Parallel SCP.
 
 #set -x
+set -u
+
+# Exit codes
+readonly EXIT_SUCCESS=0
+readonly EXIT_USAGE=1
+readonly EXIT_DEPENDENCY=4
+readonly EXIT_HOSTS_LIST=6
+readonly EXIT_HOSTS_DEAD=7
+readonly EXIT_CONNECTION=8
 
 print_usage()
 {
@@ -29,6 +38,10 @@ print_usage()
 # Parse the optional arguments
 while [ $# -gt 2 ] ; do
   case $1 in
+    "-h")
+      print_usage
+      exit $EXIT_SUCCESS
+      ;;
     "-l")
       LOGIN="$2"
       shift
@@ -58,7 +71,7 @@ done
 # "-P" as hosts' list and "my_file" as the file to be transfered.
 if [ $# -lt 2 ] ; then
   print_usage
-  exit 1
+  exit $EXIT_USAGE
 fi
 
 # Check the usage of -r and -R
@@ -67,7 +80,7 @@ if [ "$DELETE" = "1" ] ; then
     echo "Use either -r or -R, but not both!"
     echo
     print_usage
-    exit 2
+    exit $EXIT_USAGE
   fi
   RSYNC=1
   DELETE="-X --delete"
@@ -85,14 +98,16 @@ PRSYNC=$(command -v parallel-rsync || command -v prsync)
 MULTIPING=$(command -v multiping)
 if [ -z "$RSYNC" ] && [ -z "$PSCP" ] ; then
   echo "Parallel SSH (pssh) is required for this script to work."
-  exit 4
-elif [ -z "$PRSYNC" ] ; then
+  exit $EXIT_DEPENDENCY
+fi
+if [ -z "$PRSYNC" ] ; then
   echo "Parallel rsync (prsync) is required for this script to work."
-  exit 5
-elif [ -z "$MULTIPING" ] ; then
+  exit $EXIT_DEPENDENCY
+fi
+if [ -z "$MULTIPING" ] ; then
   echo "multiping (which should have been provided along with this"
   echo "script) is required for this script to work."
-  exit 6
+  exit $EXIT_DEPENDENCY
 fi
 
 # Hosts' list file
@@ -105,7 +120,7 @@ shift
 echo "Using file '$HOSTS' as hosts' list."
 if [ ! -f "$HOSTS" ] ; then
   echo "The hosts' list file doesn't exist or is not a regular file."
-  exit 3
+  exit $EXIT_HOSTS_LIST
 fi
 
 # Login
@@ -115,19 +130,19 @@ if [ -n "$LOGIN" ] ; then
   LOGIN="-l $LOGIN"
 fi
 
-# Test the connection to the first host and get the destination
+# Test the connection to the first alive host and get the destination
 # directory (home directory of the remote user)
 FIRST_HOST=$($MULTIPING "$HOSTS_LIST_NAME" 2>/dev/null \
            | sed -n "s/ is alive$//p" | head -n1)
 if [ -z "$FIRST_HOST" ] ; then
   echo "None of the remote hosts is alive."
-  exit 7
+  exit $EXIT_HOSTS_DEAD
 fi
 echo "Testing connection to $FIRST_HOST..."
 DEST_DIR="$(ssh "${SSH_LOGIN}${FIRST_HOST}" 'echo $HOME' 2>/dev/null)"
 if [ -z "$DEST_DIR" ] ; then
   echo "Cannot connect to the first alive host. Aborting."
-  exit 7
+  exit $EXIT_CONNECTION
 fi
 echo "Destination directory: $DEST_DIR"