cmp

Additional Notes

cmp compares two files byte by byte and reports the first difference. It works for both text and binary files.

Use it when you need a quick answer to whether files are identical, or where the first byte-level difference occurs.

Syntax

cmp [options] file1 file2 [skip1 [skip2]]

Parameters

• file1: First file to compare.
• file2: Second file to compare.
• skip1: Optional number of bytes to skip in file1.
• skip2: Optional number of bytes to skip in file2.
• options: Output and byte-display controls.

Common Options

• -s: Silent mode. Use exit status only.
• -l: Print byte numbers and differing byte values.
• -b: Print differing bytes.
• -i SKIP: Skip initial bytes. Some versions support SKIP1:SKIP2.
• -n LIMIT: Compare at most LIMIT bytes.

Examples

cmp file1.bin file2.bin

Report the first byte difference.

cmp -s file1 file2 && echo same || echo different

Use exit status in a script.

cmp -l old.bin new.bin | head

Show byte-level differences.

cmp -n 512 boot-a.img boot-b.img

Compare only the first 512 bytes.

Practical Notes

• Use diff for readable text differences.
• Use sha256sum when comparing files across systems or at different times.
• cmp -s is useful in scripts because it produces no normal output.