Quoting Nicolas George (geo...@nsup.org):
> Le nonidi 29 messidor, an CCXXIII, Andrew McGlashan a écrit :
> > md5_1=$(md5sum $HOME_DIR/.forward|cut -d\ -f1)
> > md5_2=$(md5sum $wrk_dir/$fix_name/.forward|cut -d\ -f1)
>
> You can write "md5="${md5%% *}" instead of using cut, one fork+exec less.
>
> And you can write "md5sum < file" to have a dash instead of the file name,
> and therefore not need to remove it.
>
> This is minor in this case, but in newly written code, avoid MD5, better
> use SHA-2.
>
> And of course (unless the files are large (unlikely for .forward) and on the
> same mechanical drive), cmp file1 file2 is much simpler.
I may've missed something here. I can't think why computing the
md5/sha-2 digest would ever be better or simpler than cmp, even
if the files are large and/or on the same spindle).
In fact I can't think why you'd ever compute a digest just to
throw it away like this:
> > if [ "$md5_1" != "$md5_2" ]
(with no further usage).
It's obviously beneficial if one of the files is remote and the
digest is being computed by the remote host at a speed greater than
the network could transfer it, but that's not the case with this
simple script, is it.
When I say beneficial, I mean in the case where most of the files
are likely to be identical. Otherwise, I don't see how anything
can be faster than cmp --quiet because cmp quits at the first
difference, viz:
$ time cat /usr/src/linux-source-3.16.tar.xz > /dev/null
real 0m8.621s
user 0m0.004s
sys 0m0.136s
$ time cat /usr/src/linux-source-3.16.tar.xz | cmp --quiet - ~/.bashrc
real 0m0.433s
user 0m0.000s
sys 0m0.000s
(both preceded by # echo 3 > /proc/sys/vm/drop_caches of course)
Cheers,
David.
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