Finding common value across multiple files containing single column values

Question

I have 100 text files containing single columns each. The files are like:

file1.txt
10032
19873
18326

file2.txt
10032
19873
11254

file3.txt
15478
10032
112         


        

Answer 1

One using Bash and comm because I needed to know if it would work. My test files were 1, 2 and 3, hence the for f in ?:

f=$(shuf -n1 -e ?)                     # pick one file randomly for initial comms file

sort "$f" > comms 

for f in ?                             # this time for all files
do 
  comm -1 -2 <(sort "$f") comms > tmp  # comms should be in sorted order always
  # grep -Fxf "$f" comms > tmp         # another solution, thanks @Sundeep
  mv tmp comms
done