Avoid duplicates in bash history | bash history duplicates
Sometimes when working, specially when writing and testing scripts, I have the need to work in the $SHELL and repeat the same commands over and over as a matter of fact if I check my $HISTORY for a command I find something like similar to :
592 vim script.sh 593 chmod +x script.sh 594 ./script.sh 595 vim script.sh 596 ./script.sh 597 vim script.sh 598 ./script.sh 599 vim script.sh 600 ./script.sh 601 vim script.sh 602 ./script.sh 603 vim script.sh 604 ./script.sh 605 vim script.sh 606 ./script.sh 607 vim script.sh 608 ./script.sh 609 vim script.sh 610 ./script.sh 611 ./script.sh
I guess you got an idea as this comes from my work computer as I’m deep in some serious scripting these days, not very handy nor very elegant either as everytime I need to search for a command I used a while back I’m forced to grep through the results or use CTRL + r as I cannot force myself to use “!!” or something history command itself.
While looking for a solution for bash history duplicates I came came across a section of the bash man page that described exactly what I was looking for.
Add the following line to your .bashrc file so that the $SHELL will not keep in history duplicates of the same command as I did above :
# User specific aliases and functions export HISTCONTROL=erasedups:ignoredups
So what this line does? Well ignoredups simply tells bash history to ignore duplicates, hence making $HISTORY “nicer”, while erasedups causes all previous lines matching the current line to be removed from the history list before that line is saved. Actually there are many other switches and options that can be used but this is what I needed for my modest needs (even because 99% of the time I’m not working locally on my system 
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Here’s en except from the bash man page describing the various switches you can use in your .bashrc file to configure the shell to your needs.
HISTCONTROL A colon-separated list of values controlling how commands are saved on the history list. If the list of values includes ignorespace, lines which begin with a space character are not saved in the history list. A value of ignoredups causes lines matching the previous history entry to not be saved. A value of ignoreboth is shorthand for ignorespace and ignoredups. A value of erasedups causes all previous lines matching the current line to be removed from the history list before that line is saved. Any value not in the above list is ignored. If HISTCONTROL is unset, or does not include a valid value, all lines read by the shell parser are saved on the history list, subject to the value of HISTIGNORE. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value of HISTCONTROL.
Well I hope you will find this little trick useful, let me know your thoughts or if you have any question.
Cheers Lethe.