[Pkg-mc-devel] Bug#498123: Bug#498123: closed by Patrick Winnertz <winnie at debian.org> (cmdline history of parallel sessions)

[Michelle Konzack]

Am 2008-09-24 23:14:24, schrieb Baurzhan Ismagulov:
> This is certainly interesting. I suppose you mean history -w and history
> -a, don't you?

WRONG, it is

    history -a      # append only NEW commands from the current session
                    # to  the  ~/.bash_history  which  lock  the   file
                    # temporary and this is working since over 8 years.

    history -r      # read history from the ~/.bash_history file

> But if bash doesn't lock the file, I still don't see how
> this can be "mathematically" correct: If history -a reads the file into
> the memory and writes the new one instead, another session could still
> corrupt the file. Could you please elaborate?

Under X, open 4 XTerms and then write

in Xterm 1:   echo "XTerm 1"
in Xterm 2:   echo "XTerm 2"
in Xterm 3:   echo "XTerm 3"
in Xterm 4:   echo "XTerm 4"

then close XTerm 1 and look at the history.  You will find the last
entry

echo "XTerm 1"

now close XTerm 4 and you will see, the last entry

echo "XTerm 4"

but the previous entry

echo "XTerm 1"

is gone.  Now try to

kill -SIGTERM ${PID_OF_XTERM_2} ${PID_OF_XTERM_3}

and look in the ~/.bash_history where you will find only 

echo "XTerm 3"

since the Processes are killed in sequence and Xterm3 is overwriting the
changes from XTerm2.

While reading and writing, the ~/.bash_history will be locked and  after
read/write immediately released...

So if you create a function in your ~/.bash_login like

----[ '~/.bash_login' ]-------------------------------------
export HISTFILESIZE=1000

shopt -s cmdhist histappend histverify lithist

histupdate()
{
  history -a $1
  history -r $1
}
------------------------------------------------------------

and in the XTerm or the Console you can type 'histupdate'  and  you  are
done. Also I have added $1, which give me the option append/read to/from
a specified file.  I have had never problems with "The BaSH".

And since I hate duplicated history entries in my ~/.bash_history, I use

----[ '~/.bash_logout' ]------------------------------------
touch ~/.bash_history.tmp
(cat ~/.bash_history) |
while read LINE
do
  grep --regexp="$LINE" ~/.bash_history.tmp >/dev/null 2>&1
  if [ $? -ne 0 ] ; then
    FLAG=true
    echo -e "${LINE}" >>~/.bash_history.tmp
  fi
done
if [ "${FLAG}" = "true"] ; then
  /bin/mv -f ~/.bash_history.tmp ~/.bash_history
else
  /bin/rm -f ~/.bash_history.tmp
fi
------------------------------------------------------------

which keep the sequence  of  the  history  entries,  exactly  the  first
occurence.  OK, I have a better one which use the last enty, but this is
only interesting if you have not more entries as 100-200 and/or  a  fast
machine since it is complex and NEED ONLY "The BaSH".

Thanks, Greetings and nice Day/Evening
    Michelle Konzack
    Systemadministrator
    24V Electronic Engineer
    Tamay Dogan Network
    Debian GNU/Linux Consultant


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