Shell Programming and Scripting

hi
am having two files

more file1
a
b
c
d

more file2
a
b
c
d

i need a loop to read the 1st line from file1 and 1st line from file 2 and grep them from file3. Then go read the 2nd line and go on...

i tried to do it but it was a mess.

I am assuming 'grep from file 3' means grep -f file3, not read a record from file three to grep file 1 and file 2 records.

Code:

paste file1.txt file2.txt | grep -f file3.txt

or the other way 'round: grep single file3 record against rec1 and rec2

Code:

cnt=$( wc -l file1.txt)
> dummy1
while [[ $cnt -gt 0 ]] 
do
     echo '|' >> dummy1
     cnt=$(( cnt - 1))
done 
cp dummy1 dummy2
paste file1.txt dummy1 file2.txt dummy2 file3.txt | \
while IFS='|' && read rec1 rec2 rec3
do
       echo "$rec1"| grep  "$rec3"
       echo "$rec2" | grep "$rec3"
done

Thank you jim mcnamara

it worked "somehow", but now i ve a nother problem
ive input file contains to clums a and b spreated by pipe
a | b
123|456
323|455

and
xyz contains other info about a and b

now i want to print as follows:

a | b | "info from xyz"

but "info from xyz" might be more than 1 line and i want to keep the format to 3 cloums.
how to do it?
i tried the belw script but printing was worng.