Shell Programming and Scripting

USEROLD=`cat oldusers`
USERNEW=`cat newusers`
USEROLDARRAY=( $USEROLD )
USERNEWARRAY=( $USERNEW )
arraylength=`cat oldusers | wc -l`
i=0;
while [ "$i" -lt "$arraylength" ]
do
        fromold=${USEROLDARRAY["$i"]};
        fromnew=${USERNEWARRAY["$i"]};
        echo "Replacing $fromold with $fromnew"
        cat groups.almost | sed s/$fromold/$fromnew/g >> tmpfile
        mv tmpfile groups.almost
 
let "i = $i +1"
done
mv groups.almost groups.final

sed 's/\b$old\b/$new/g'

awk '
FILENAME=="newusers.txt"{a[FNR]=$0}
FILENAME=="oldusers.txt"{b[$0]=a[FNR]}
FILENAME=="groups.txt"{
             l=split($NF,c,",");$NF="";
             for(i=1;i<=l;i++) $NF=(c[i] in b)?$NF","b[c[i]]:$NF","c[i];
             sub(",","",$NF);print}
' newusers.txt oldusers.txt FS=':' OFS=':' groups.txt
mygroup1:x:1:dlin,blin,clin
mygroup2:x:2:jbob,jaim,jjohn
mygroup3:x:3:bylin,klin,jlin