cmp vs diff vs comm on Linux: Which File Comparison Tool to Use

Operators search for cmp vs diff when a script must know whether two files are identical (release tarball, checksum policy) versus what changed (config review). comm is a third tool: it answers set questions on already-sorted lists — not a full diff.

Deep dives: diff,
comm,
sha256sum.

cmp — byte-by-byte identity

cmp stops at the first differing byte; exit 0 if identical, 1 if not — ideal for automation.

cmp -s fileA fileB && echo same || echo different
cmp -l fileA fileB | head   # list differing bytes

diff — line-oriented changes

diff -u shows unified patches for humans and patch; use when you need context, not just yes/no.

diff -u /etc/nginx/nginx.conf /tmp/nginx.conf.new | head

comm — sorted set logic

Requires sorted input. comm -12 = lines in both; -23 = only in file2. Faster mental model than diff for username/package lists.

sort -u old-users.txt > /tmp/a
sort -u new-users.txt > /tmp/b
comm -12 /tmp/a /tmp/b

Comparison cheat sheet

Binary identity → cmp or sha256sum. Readable changelog → diff. Two sorted columns → comm.

Quick Reference

• Identical files: cmp -s a b
• What changed: diff -u a b
• Sorted overlap: comm -12 a b

Related tutorials

• diff guide
• comm guide
• checksums

Diagrams are original illustrations by Gnome IT Solutions. Tutorial text © Gnome IT Solutions.