| # add already existing file to zip, making duplicate names | |
| program modify | |
| return 1 | |
| args testfile.zip add_file testfile.txt testfile.txt 0 -1 | |
| file testfile.txt testfile.txt testfile.txt | |
| file testfile.zip testfile.zip testfile.zip | |
| stderr can't add file `testfile.txt': File already exists |