Maintain permissions bits when writing new file with VIM

Question

In Vim, when I write a copy of the current buffer to a new file using :w [filename], it appears that Vim uses the default (i.e. set by umask or whatever) file permissions for the new file. If the current buffer was loaded from an existing file, though, shouldn't the "right" behavior be to duplicate the permissions from that file? For example, if I'm editing an executable file, and I write a new copy of the file, why doesn't Vim write a new executable? Is there any way to force Vim to behave the way I'm describing, other than just doing something like ! chmod --reference % [newfilename] after writing the new file?

Answer 1

You could do something like this. First, capture the name of the original file.

au BufRead * let b:oldfile = expand("<afile>")

Then, when you save the new file, change its permissions to be the same as those of the original file.

au BufWritePost * if exists("b:oldfile") | let b:newfile = expand("<afile>") | if b:newfile != b:oldfile | echo system("chmod --reference=".b:oldfile." ".b:newfile) | endif |endif

Just put both of those autocommands into your ~/.vimrc.

Answer 2

Make sure that there are no unsaved changes in the file and then use cp to make a copy. That will result in a copy with the same permissions as the original.