We need to implement the same exit codes than unzip.

From the man page:

Diagnostics

• 0: normal; no errors or warnings detected.
• 1: one or more warning errors were encountered, but processing completed successfully anyway. This includes zipfiles where one or more files was skipped due to unsupported compression method or encryption with an unknown password.
• 2: a generic error in the zipfile format was detected. Processing may have completed successfully anyway; some broken zipfiles created by other archivers have simple work-arounds.
• 3: a severe error in the zipfile format was detected. Processing probably failed immediately.
• 4: unzip was unable to allocate memory for one or more buffers during program initialization.
• 5: unzip was unable to allocate memory or unable to obtain a tty to read the decryption password(s).
• 6: unzip was unable to allocate memory during decompression to disk.
• 7: unzip was unable to allocate memory during in-memory decompression.
• 8: [currently not used]
• 9: the specified zipfiles were not found.
• 10: invalid options were specified on the command line.
• 11: no matching files were found.
• 50: the disk is (or was) full during extraction.
• 51: the end of the ZIP archive was encountered prematurely.
• 80: the user aborted unzip prematurely with control-C (or similar)
• 81: testing or extraction of one or more files failed due to unsupported compression methods or unsupported decryption.
• 82: no files were found due to bad decryption password(s). (If even one file is successfully processed, however, the exit status is 1.)