Merging files into a single tab delimited file with a space separating

I have a folder that contains say 50 files in a sequential order:

cdf_1.txt
cdf_2.txt
cdf_3.txt
cdf_3.txt
.
.
.
cdf_50.txt.

I need to merge these files in the same order into a single tab delimited file.

I used the following shell script:

for x in {1..50};
  do cat cdf_${x}.txt >> All.txt;
done

This will merge the files in the same order and out put the All.txt.

What I need is to give a space between the contents of files in the All.txt so that I could know the contents of each file separately in the All.txt.

Is there a way to modify the above shell script to give a space between the content of every file?

Please let me know.

Something like this:

for f in cdf_*.txt; do
  printf '%s\n\n' "$(<"$f")"
done > All.txt

If you are looking to put just one line between each file catted then try this

for x in {1..50}
do
  cat cdf_${x}.txt >> all.txt
  echo >> all.txt
done

Or (a little easier if you are doing many things):

for x in {1..50}
do
  cat cdf_${x}.txt 
  echo 
done > all.txt

and you do need bash 3 for that loop to work; older shells might be able to use "seq",