diff --git a/hangover.sh b/hangover.sh
index 800a182..d3ab4c8 100755
--- a/hangover.sh
+++ b/hangover.sh
@@ -1,7 +1,7 @@
-#!/bin/sh -e
+#!/bin/bash -e
 
 # Exit early if any session with my username is found
-if who | grep -wq $USER; then
+if who | grep -wq "^$USER"; then
   exit
 fi
 
@@ -15,18 +15,19 @@ EXCUSES=(
   'Food poisoning'
   'Not feeling well'
 )
-rand=$[ $RANDOM % ${#EXCUSES[@]} ]
+rand=$(( RANDOM % ${#EXCUSES[@]} ))
 
 RANDOM_EXCUSE=${EXCUSES[$rand]}
 MESSAGE="Gonna work from home. "$RANDOM_EXCUSE
 
 # Send a text message
-RESPONSE=`curl -fSs -u "$TWILIO_ACCOUNT_SID:$TWILIO_AUTH_TOKEN" \
+RESPONSE=$(curl -fSs -u "$TWILIO_ACCOUNT_SID:$TWILIO_AUTH_TOKEN" \
   -d "From=$MY_NUMBER" -d "To=$NUMBER_OF_BOSS" -d "Body=$MESSAGE" \
-  "https://api.twilio.com/2010-04-01/Accounts/$TWILIO_ACCOUNT_SID/Messages"`
+  "https://api.twilio.com/2010-04-01/Accounts/$TWILIO_ACCOUNT_SID/Messages")
 
 # Log errors
-if [ $? -gt 0 ]; then
+if (( $? > 0 )); then
   echo "Failed to send SMS: $RESPONSE"
   exit 1
 fi
+