Bash, how to print out that files are the same when using cmp

Question

cmp file1 file2 does nothing when the files are the same. So how do I print out that files are the same in shell script?

Answer 1

The exit status of cpm is zero if the files are identical, and non-zero otherwise. Thus, you can use something like

cmp file1 file2 && echo "Files are identical"

If you want to save the exit status, you can use something like the following instead:

cmp file1 file2
status=$?
if [[ $status = 0 ]]; then
    echo "Files are the same"
else
    echo "Files are different"
fi

Answer 2

Use the exit status code of cmp. Exit codes of 0 mean they're the same:

$ cmp file1 file2; echo $?
0

In a script you can do something like this:

cmp file1 file2 && echo "same"

Answer 3

If you just need to display the result, you can also use diff -q -s file1 file2:

• The -q option (AKA --brief) makes diff work similarly to cmp, so that it only checks whether the files are different or identical, without identifying the changes (Note: I don't know if there's a performance difference between this and cmp).
• The -s option (AKA --report-identical-files) makes it display a "Files file1 and file2 are identical" message rather than giving no output. When the files differ, a "Files file1 and file2 differ" message is shown either way (assuming -q is used).

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