Re: [9fans] dumb question

[Boyd Roberts <boyd@strakt.com>]

Lucio De Re wrote:
> I keep promising myself I'll write a "stat" modelled on "du" that
> produces a record of stat fields for each entry in the descended
> directory.

I did this once so I could build a magnetic version of /n/dump on ULTRIX.

I wanted to hang onto files modified in the 'recent past' so I needed
something to get at the stat information and then use this to decide
what files to copy (based on type, mtime, size, name, ...).

So I wrote 'walk' and implemented an /n/dump file tree writer as:

    walk | select | push

walk was program as it had to call ftw(3), but the others were scripts.

select contained the logic for deciding if a file was worth copying
and if so it output the name of the file.  I also had a plan that
select could be user supplied, but I never implemented it.

push would copy filenames read from stdin to /n/dump/YYYY/MMDD/...

All 3 ran as the user whose home directory was being copied.  This
was imperfect, but it was secure.  The controlling script used 'su'
to become the user, avoiding the yet another program running as root
syndrome.

Time information output by walk was represented as a numeric value
to avoid re-parsing problems and it was never intended to be read
by humans.  Anyway, it's a trivial exercise to write a filter to
mung the output of walk.

As far as quoting went I think i decided that if you were stupid
enough to name your files with newlines you didn't deserve to get
them copied.  select would catch some of these or push would get
'No such file or directory'.  The name of the file was output
last by walk, after the stat info.

This version of /n/dump was just a convenience so loss of data
was no big drama (the standard backup system would catch that).

The hardest part was getting the script to glue 4 RA-90's [1Gb each]
together so that the last month of stuff was kept/recycled.
Teaching shell scripts about time is no fun.