Linux diff exit code when using the less pager

Retrieve the diff exit code when using diff with the less pager.

The diff command returns an exit code of 0 when there is no difference and 1 when there is a difference.

No difference with exit code of 0:

$ diff <(echo "abc") <(echo "abc") > /dev/null; echo "exit code: $?"

exit code: 0

Difference with exit code of 1:

$ diff <(echo "abc") <(echo "def") > /dev/null; echo "exit code: $?"

exit code: 1

Solution: Save the diff result to a variable and use its exit code:

diff_result="$(diff --recursive --unified file1.txt file2.txt)"
exit_code="$?"
if [[ "${exit_code}" -eq 0 ]]; then
    echo "files are identical"
else
    echo "${diff_result}" | less -R
    echo "differences found"
fi

kw: diff, file descriptor, process substitution, anonymous pipe