diff --help

diff --version

cat abc.txt
cat def.txt

diff abc.txt def.txt

diff -c abc.txt def.txt

diff -c abc.txt def.txt > diff.txt

diff -u abc.txt def.txt

diff -i abc.txt def.txt

cat 123.txt
cat 456.txt

diff -i 123.txt 456.txt

diff -r mv snap