2 while read loops?

Question

So the object of the script I'm making is to compare files from two while read lists that have file path names in them...

while read compareFile <&3; do     
 if [[ ! $server =~ [^[:space:]] ]] ; then  #empty line exception
  continue
 fi   
    echo "Comparing file - $compareFile"
 if diff "$compareFile" _(other file from loop?_) >/dev/null ; then
    echo Same
 else
     echo Different
 fi   
 done 3</infanass/dev/admin/filestoCompare.txt

I need to be able to compare files from two different lists at the same time through two while read loops... Is this even possible?

Answer 1

Not really understand what you want achieve, but the next:

while read -r file1 file2
do
    echo diff "$file1" "$file2"
done < <(paste <(grep . list1.txt) <(grep . list2.txt))

where the list1.txt contains:

file1.txt
file2.txt

file3.txt

file4.txt
file5.txt

and the list2.txt contains:

another1.txt

another2.txt
another3.txt
another4.txt

another5.txt

produces the next output:

diff file1.txt another1.txt
diff file2.txt another2.txt
diff file3.txt another3.txt
diff file4.txt another4.txt
diff file5.txt another5.txt

Remove the echo before the diff if you satisfied.

Answer 2

while read newfile <&3; do   
 if [[ ! $newfile =~ [^[:space:]] ]] ; then  #empty line exception
    continue
 fi   
 #
 while read oldfile <&3; do   
 if [[ ! $oldfile =~ [^[:space:]] ]] ; then  #empty line exception
    continue
 fi   
    echo Comparing "$newfile" with "$oldfile"
    #
    if diff "$newfile" "$oldfile" >/dev/null ; then
      echo The files compared are the same. No changes were made.
    else
        echo The files compared are different.
        #
    fi    
  done 3</home/u0146121/test/oldfiles.txt
 done 3</home/u0146121/test/newfiles.txt

Answer 3

I think I would restructure that along these lines:

while true
do
   read -u3 line1 || break
   read -u4 line2 || break

   # do whatever...
done 3< file1 4< file2

That uses a single loop, and will exit that loop when end of file is reached on either input file. The logic would be a little more complicated if you want to read both files entirely, even if one ends early...

Answer 4

if I understand you correctly...yes. Here's an example of looping through two files in lock-step

exec 3<filelist1.txt
exec 4<filelist2.txt
while read -r file1 <&3 && read -r file2 <&4; do echo ${file1}","${file2}; done
exec 3>&- 4>&-