On Wed, Jan 18, 2012 at 6:19 AM, Teika Kazura <te...@lavabit.com> wrote: > > Hi. When you edit a running bash script, it's affected, so you > shouldn't do that [1][2]. However, I heard[3] that if you delete the > script itself from the filesystem, the original is remembered by bash, > and it continues to run as-is (as-was?). It seems correct as far as I > tried several times. > > What's the, or are there any rationale for this difference? If the > entire script is read at invocation, then why should / does > modification affect? Is it a bug? >
It's due to the way unix works, if you look at the documentation of unlink, for instance in the posix man page: "When the file's link count becomes 0 and no process has the file open, the space occupied by the file shall be freed and the file shall no longer be accessible. If one or more processes have the file open when the last link is removed, the link shall be removed before unlink() returns, but the removal of the file contents shall be postponed until all references to the file are closed." You'll notice that your are not really deleting a file, you are decrementing a counter by one. So what you do when you delete the file is that you remove one link, since bash has it open to execute the script there is still a reference to the old script and bash continues normally. If you edit the file bash is reading, then everything can happen, you might edit a portion of the file that bash has read but not yet executed for instance (since io is buffered).
