This tool uses the POSIX ftruncate function to set the length of a file.
- If the file exists and is longer than that, it will be truncated (bytes after that length cut off).
- If the file exists and is shorter than that, it will be extended and the new bytes zero-filled. (Whether this actually consists of writing zero-bytes to disk is dependent on your operating system's implementation.)
- If the file doesn't already exist, it will be created, then extended to the desired length.
This is a very handy way to instantly create raw disk images for emulators. You can do things like truncate 1G oneBEELLIONbytes.img to create a blank disk image that you can then format with either host tools (like newfs_hfs or newfs_msdos) or guest tools (like the built-in Initialize alert in classic Mac OS).
Sizes can be specified as either whole numbers of bytes or whole numbers followed by a suffix:
- B (or no suffix)
- Bytes
- S
- Sectors of 512 bytes each)
- K
- Kibibytes (KiB) of 1024 bytes each
- M
- Mebibytes (MiB): 1024**2 = 1048576 bytes
- G
- Gibibytes (GiB): 1024**3 = >1 billion bytes
- T
- Tebibytes (TiB): 1024**4 = >1 triillion bytes
- P
- Pebibytes (PiB): 1024**5 = 1024 tebibytes
- E
- Exbibytes (EiB): 1024**6 = 1048576 tebibytes
- Z
- Zebibytes (ZiB): 1024**7
- Y
- Yobibytes (YiB): 1024**8
This works on macOS. It should work on, or at least be portable to, Linux-based operating systems.