Intersection of two lists in Bash

Question

comm -12  <(ls 1) <(ls 2)

Solution with comm

comm is great, but indeed it needs to work with sorted lists. And fortunately here we use ls which from the ls Bash man page:

Sort entries alphabetically if none of -cftuSUX nor --sort.

comm -12  <(ls one) <(ls two)

Alternative with sort

Intersection of two lists:

sort <(ls one) <(ls two) | uniq -d

Symmetric difference of two lists:

sort <(ls one) <(ls two) | uniq -u

Bonus

Play with it ;)

cd $(mktemp -d) && mkdir {one,two} && touch {one,two}/file_{1,2}{0..9} && touch two/file_3{0..9}

Use the comm command:

ls one | sort > /tmp/one_list
ls two | sort > /tmp/two_list
comm -12 /tmp/one_list /tmp/two_list

"sort" is not really needed, but I always include it before using "comm" just in case.

A less efficient (than comm) alternative:

cat <(ls 1 | sort -u) <(ls 2 | sort -u) | uniq -d

Join is another good option depending on the input and desired output

join -j1 -a1 <(ls 1) <(ls 2)