CODE EXAMPLE FOR SHELL

preserve bash history

# Maximum number of history lines in memory
export HISTSIZE=50000
# Maximum number of history lines on disk
export HISTFILESIZE=50000
# Ignore duplicate lines
export HISTCONTROL=ignoredups:erasedups
# When the shell exits, append to the history file 
#  instead of overwriting it
shopt -s histappend

# After each command, append to the history file 
#  and reread it
export PROMPT_COMMAND="${PROMPT_COMMAND:+$PROMPT_COMMAND$'n'}history -a; history -c; history -r"