Re: Dynamically changing remote servers list

[Douglas A. Augusto]

On 28/08/2014 at 00:38,
Ole Tange <ole@tange.dk> wrote:

> You should test that it works with all the supported styles of
> sshlogins. From the man page:

Hi,

I made the script more robust and it now seems to support all the styles of
sshlogins: 

################################################################################
   cp original.slf updated.slf
   while [ 1 ] ; do
      nice parallel --timeout 1000% --nonall -j0 -k --slf original.slf --tag 
echo | \
         sed -e 's#\t$##' -e '#\t#d' | \
         nice parallel -k "sed -n 's#^\([[:digit:]]\+/\)\{0,1\}{}\$#&#p' 
original.slf | head -n 1" > tmp.slf
      if ! cmp -s tmp.slf updated.slf; then
         mv tmp.slf updated.slf
      fi
   
      sleep 10
   done &

   parallel --slf updated.slf ...
################################################################################

The command which, given a sshlogin string, recovers the full entry from the
original slf file (original.slf) is:

    "sed -n 's#^\([[:digit:]]\+/\)\{0,1\}{}\$#&#p' original.slf | head -n 1"

Basically, it assembles a matching pattern that begins with the optional
specification of the number of slots (will match e.g. "16/" or none):

   ^\([[:digit:]]\+/\)\{0,1\}

then it appends the sshlogin string at hand until the end of the line:

   {}\$

finally, the corresponding matched pattern (full entry) is printed by

   #&#p


##########

There are two minor limitations, though:

   1) If the original.slf contains duplicate entries differing only by the
specification of the number of slots, such as: 

   server.net
   8/server.net

only the first one will be picked (this is what 'head -n 1' does).

   2) I'd like to prevent the replacement {} from being quoted by GNU Parallel,
but it insists on converting something like:

   ssh -p 2222 server.domain.net

into

   ssh\ -p\ 2222\ server.domain.net

This by itself doesn't seem to be a problem within sed. The problem is that I
cannot quote the dots in server.domain.net (making it server\.domain\.net,
turning off their special meaning within sed) because GNU Parallel overrides
any attempt of doing so. For instance, the following would work:

   parallel --rpl '{quote} s#\.#\\.#g' -k "sed -n 
's#^\([[:digit:]]\+/\)\{0,1\}{quote}\$#&#p' original.slf | head -n 1"

but only if replace this line:

   my $cmdstring = 
$self->replace_placeholders($self->{'command'},$Global::quoting,$quote_arg);

by

   my $cmdstring = 
$self->replace_placeholders($self->{'command'},$Global::quoting,0);

in GNU Parallel's source code. Am I missing something?

-- 
Douglas A. Augusto