Re: Why isn't there a "copy" function?

[iburrell]

Because Unix does not have a copy function. Doing a file copy requires extra code, which is in File::Copy. This isn't too inconsistent since file moves across filesystems requires similar support, like with File::Copy::move.

A better question is why Unix does not have a copy function to copy files. The operating system can do a better job copying files than user code. It can be much more efficient with network file systems, knows more about file attributes, better optimize IO, and could implement copy-on-write behavior. A copy() that only worked within a filesystem would be similar to rename().

[Anonymous Monk]

Consideration is currently going into Linux to add sendfile file-to-file semantics, which would be basically equivalent to a copyfile system call. The major problem is that, if you were to copy a 2GiB file, for example, it would freeze the system as the kernel took up all available processing time doing the copy. So, copyfile system calls would tend to expose a local DoS attack, because they happen in a place where execution can't normally be interrupted to allow for multitasking.

[mce]

Good point,
On unix, File::Copy needs to be called when moving a file, but on Windows Win32::FileCopy is more reliable.
copy-ing a file works best when the direct OS API's are called. (has to do with file permissions etc... ).

[Anonymous Monk]

On unix, File::Copy needs to be called when moving a file,

If you like to be surprised or use non-flexible API, you'd use File::Copy. If you're smart, you'd use system cp. Things that are easy with system cp and awkward with File::Copy include:

    cp file1 file2 dir
    cp -r dir1 dir2
    cp -p file1 file2
    cp exe1 exe2

Not to mention that I can stick an 'r' or an 's' in front of it, and copy from one machine to another.

[eserte]

Unfortunately system(qw(cp ...)) is not portable. That's why there is File::NCopy, which I would like to see in the perl core instead of File::Copy.