Most efficient but sort files first


diff $1 $2 | grep "^<" | sed 's/< //'




 
#!/bin/bash

#Get original internal field separator
ORIGIFS=$IFS

#set original internal field separator to end-of-line
IFS=`echo -en "\n\b"`


for i in `cat $1`
do
  MYFOUND="NO"
  for y in `cat $2`
  do
    if [[ "$i" == "$y" ]]
    then
      MYFOUND="YES"
      break
    fi
  done

  if [[ "$MYFOUND" == "NO" ]]
  then
    echo $i
  fi

done

#set original internal field separator back to original
IFS=$ORIGIFS



or with arrays


#!/bin/bash

IFS=`echo -en "\n\b"`

myfile1=( $( < $1 ) )
myfile2=( $( < $2 ) )

for i in ${myfile1[[@]]}
do
  MYFOUND="NO"
  for y in ${myfile2[[@]]}
  do
    if [[ "$i" == "$y" ]]
    then
      MYFOUND="YES"
      break
    fi
  done

  if [[ "$MYFOUND" == "NO" ]]
  then
    echo $i
  fi

done