On Tue, Feb 26, 2008 at 9:09 PM, David Korn <[EMAIL PROTECTED]> wrote:
> Yes, this already exists, you can do
>
> $ nl myfile | iconv -fL1 -tUTF-8 1<> myfile
>
> <> opens the file for reading and writing. The default is file descriptor
> is 0.
>
> tr [A-Z] [a-z] < file 1<> file
:-) Thanks. "In-place" was probably the wrong word I used, since
it should reliably work for expanding also, as Icarus points out.
The operator might act somewhat like &&> (although this already
has another meaning). On the left of it, there is an implicit set -o
pipefail, and on the right, the file is only created on success, and
is guaranteed to have a different inum. That means a temporary file
must be created first, and then on success, the old one gets unliked
(possibly implicitly by rename).
While my initial idea was to type less, I think similar mechanisms
are also used to replace files that are potentially actively used: pages
on a web server, binaries and shared libraries (although they probably
do an additional backup step first -- but still, the file is replaced in
one operation instantly). So the whole thing is like a transaction,
and if the pipe failed, nothing happened (the old file is still there),
it's "rolled back". And I could also easily check that by comparing
the inum (say, if another process doesn't know the exit status).
And I wouldn't have to worry about file locking, etc. -- that would
be done without my knowing, if necessary.
Well, just an idea... I don't want to turn it into a database. :-)
Thanks,
Markus
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