bash enhancements: history

[Peter]

I had proposed that various instances of bash exit and save their 
respective histories in the ~/.bash_history file. I think that I found a 
way to do this (error checking omitted in code below):

 	fd = open( "~/.bash_history", O_RDWR|O_CREAT, S_IRUSR|S_IWUSR );
 	flock( fd, LOCK_EX );
 	append_history( history_length, "~/.bash_history" );
 	flock( fd, LOCK_UN );
 	close( fd );

this is simple enough to patch into bash, no ? (is this use of flock 
safe ? what if append_history uses flock() itself ?) The issue of 
identifying the instance in the saved history list is not addressed. It 
could be addressed by adding a log entry like:

 	now = time();
 	sprintf( buf, "# %s: bash(%d) exiting", ctime( &now ), getpid() );
 	add_history( buf );

before running the code above. When loaded in the history of a next 
instance it would appear as a comment line and do nothing if recalled by 
mistake. A similar entry could be added to the history when the shell 
starts (immediately after using_history(); ), with the effect of 
bracketing the commands used by a certain instance.

Peter
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