Re: sed --in-place bug (updates mtime of file even if no changes are made)

[John Vanderpool]

On 11/11/11 19:35, Eric Blake wrote:
> On 11/08/2011 02:32 PM, John Vanderpool wrote:
> > --in-place shouldn't update the mtime of the file if the pattern doesn't
> > match
> > (i.e. no changes were made to file)
> Why not?  Conceptually, 'sed --in-place' is short-hand for 'sed>  temp,
> mv temp original', since it is not possible to known a priori whether
> the sed script will modify the input when generating the temporary file.
>
> You're welcome to submit a patch if you think you can fix it, but right
> now, I don't think sed should have to recognize whether the output is
> identical to the input.  If you need mtime unchanged, then use sed to a
> temporary file yourself, and compare the two files before deciding
> whether to move the temporary file or keep the original.

thanx for your time replying.

My C programming is a little rusty (like 20 years!) so don't think I should
muck with the code.  Possibly a mention in man page would be prudent
though? (see bottom)

here is how this came to light, a very senior SA had the task of changing a
NASA mandated mail list from one name to another and the name was all
over the systems so he ran:

find / -type f -exec sed --in-place 's/address@hidden/address@hidden/' {} \;

and boom, every file on the systems all had the current date - ouch!

----------------------

possible man page change:

       -i[SUFFIX], --in-place[=SUFFIX]

              edit files in place (makes backup if extension supplied)
              WARNING: input file's mtime is updated regardless of if sed made any 
changes or not