Node:Backups, Next:Backup Names, Previous:patch Directories, Up:Merging with patch

### Backup Files

Normally, `patch` creates a backup file if the patch does not exactly match the original input file, because in that case the original data might not be recovered if you undo the patch with `patch -R` (see Reversed Patches). However, when conforming to POSIX, `patch` does not create backup files by default. See patch and POSIX.

The `-b` or `--backup` option causes `patch` to make a backup file regardless of whether the patch matches the original input. The `--backup-if-mismatch` option causes `patch` to create backup files for mismatches files; this is the default when not conforming to POSIX. The `--no-backup-if-mismatch` option causes `patch` to not create backup files, even for mismatched patches; this is the default when conforming to POSIX.

When backing up a file that does not exist, an empty, unreadable backup file is created as a placeholder to represent the nonexistent file.