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I really enjoying using control+r to recursively search my command history. I've found a few good options I like to use with it:

# ignore duplicate commands, ignore commands starting with a space
export HISTCONTROL=erasedups:ignorespace

# keep the last 5000 entries
export HISTSIZE=5000

# append to the history instead of overwriting (good for multiple connections)
shopt -s histappend

The only problem for me is that erasedups only erases sequential duplicates - so that with this string of commands:

ls
cd ~
ls

The ls command will actually be recorded twice. I've thought about periodically running w/ cron:

cat .bash_history | sort | uniq > temp.txt
mv temp.txt .bash_history

This would achieve removing the duplicates, but unfortunately the order would not be preserved. If I don't sort the file first I don't believe uniq can work properly.

How can I remove duplicates in my .bash_history, preserving order?

Extra Credit:

Are there any problems with overwriting the .bash_history file via a script? For example, if you remove an apache log file I think you need to send a nohup / reset signal with kill to have it flush it's connection to the file. If that is the case with the .bash_history file, perhaps I could somehow use ps to check and make sure there are no connected sessions before the filtering script is run?

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Try ignoredups instead of erasedups for a while and see how that works for you. –  jw013 Sep 20 '12 at 15:54
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I don't think bash holds an open file handle to the history file - it reads/writes it when it needs to, so it should (note - should - I haven't tested) be safe to overwrite it from elsewhere. –  D_Bye Sep 20 '12 at 19:00
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3 Answers

up vote 11 down vote accepted

Sorting the history

This command works like sort|uniq, but keeps the lines in place

nl|sort -k 2|uniq -f 1|sort -n|cut -f 2

Basically, prepends to each line its number. After sort|uniq-ing, all lines are sorted back according to their original order (using the line number field) and the line number field is removed from the lines.

This solution has the flaw that it is undefined which representative of a class of equal lines will make it in the output and therefore its position in the final output is undefined. However, if the latest representative should be chosen you can sort the input by a second key:

nl|sort -k2 -k 1,1nr|uniq -f1|sort -n|cut -f2

Managing .bash_history

For re-reading and writing back the history, you can use history -a and history -w respectively.

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A version of decorate-sort-undecorate, implemented with shell tools. Nice. –  ire_and_curses Sep 20 '12 at 17:21
    
With sort, the -r switch always reverses the sorting order. But this won't yield the result you have in mind. sort regards the two occurrences of ls as identical with the result that, even when reversed, the eventual order depends on the sorting algorithm. But see my update for another idea. –  artistoex Sep 20 '12 at 19:29
    
In case, you don't want to modify .bash_history, you could put the following in .bashrc: alias history='history | sort -k2 -k 1,1nr | uniq -f 1 | sort -n' –  Nathan Jan 15 at 20:35
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These would keep the last duplicated lines:

ruby -i -e 'puts readlines.reverse.uniq.reverse' ~/.bash_history
tac ~/.bash_history | awk '!a[$0]++' | tac > t; mv t ~/.bash_history
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Found this solution in the wild and tested:

awk '!x[$0]++'

I would add an explanation of the code, but I can't grok Awk yet. I welcome anyone who knows how this works to edit the post and add it in here.

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