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?

chepner · Accepted Answer · 2014-05-02T14:21:46.097

7

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

edited May 02 '14 at 14:21

answered May 02 '14 at 13:23

chepner

Can I assign the exit status of cpm to some variable in bash? – kulan May 02 '14 at 13:27
`var=$?`; just after `cmp ` – PradyJord May 02 '14 at 13:29
this will also work `if (cmp file1 file2); then echo "same"; else echo "not"; fi` – Avinash Raj May 02 '14 at 13:36
1

@AvinashRaj The parentheses are not necessary. – chepner May 02 '14 at 14:18
Shorthand for if/then/else without a variable: `cmp file1 file2 && echo "Files are identical" || echo "Files are different"` – Cole Tierney May 02 '14 at 14:40
A dangerous shorthand if used improperly; this works because `echo` always exits 0, but if the command following `&&` fails, the command following `||` is executed as well. `a && { b || true; } || c` is more correct (but uglier). – chepner May 02 '14 at 14:54

score 2 · Answer 2 · edited May 02 '14 at 13:32

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"

edited May 02 '14 at 13:32

Avinash Raj

answered May 02 '14 at 13:24

pgl

score 0 · Answer 3 · answered Sep 09 '21 at 15:16

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).

3 Answers3