Copy without overwrite in OpenWRT

Developer's Corner General Dev Discussions
1

Apologies for the stupid question! Does anyone know how to copy without overwriting a file in OpenWRT? The cp command in OpenWRT appears to have limited options and lacks the required option to not overwrite files!

I can easily check if the file exists in Lua, but this is yet another time consuming task that I’d prefer to avoid if the OS can do this.

Thanks
Chris

2

According to its --help, the cp command has the -i option. That’s the closest cp gets to “don’t overwrite”. What were you expecting?

Edit: oh, you are hoping for the GNU cp -n option. Nope, OpenWrt cp is the busybox cp, it never had all the bells and whistles of GNU.

You could string together a shell pipeline:

[ ! -e “$target” ] && cp “$source” “$target”

3

Thanks fuztle,
Yes, I was after the -n option. -i says it prompts for overwrite, which isn’t quite what I’m after. That said, I’ve not tried it from Lua, but I assume it will simply never return if run from os.execute().

It’s strange that there’s an “overwrite” option (-f), but cp seems to do this already by default!

Cheers
Chris

4

-f will overwrite a target file even if it has been marked read-only (say, with a chmod -w). Which may inspire you to an alternative approach.

5

Ah - thanks. At least that makes sense now and I may be able to use that to my advantage. I’ll have a play…

Cheers
Chris