Bash – Why does bash still keep duplicate lines with erasedups

bashcommand history

I have the following line in my ~/.bashrc

export HISTCONTROL=ignoreboth:erasedups

However whenever I run somecommand it keeps adding the duplicated command into .bash_history like this

grep -w somecommand ~/.bash_history
somecommand
somecommand abc xyz
somecommand 123
somecommand
...

Why is this and how to prevent it?

Best Answer

According to man bash:

A value of ignoredups causes lines matching the previous history entry to not be saved.

If you run somecommand twice in a row with no arguments, you should see only one consecutive entry.

Likewise if you run somecommand 123 twice in a row, it will only be added to the history once.

The commands in your list show no consecutive duplicates, so this feature is working as intended.

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Bash – Saving bash history from multiple Konsole not working correctly

I have concluded that it is not possible to append the new commands directly and at the same time to remove any duplicates. So my solution is to run the following command ones in a while. or to put it in my crontab.

tac $HOME/.bash_history | awk '!seen[$0]++' | tac > $HOME/.hist_Temp 
mv $HOME/.hist_Temp $HOME/.bash_history

The above command will keep the last occurrence of a command and remove every other repetitions above it from the history file without messing up the order.

Bash – Why does “bash -x” break this script

The problem is this line:

TIMESEC=$(echo blah | ( /usr/bin/time -f %e grep blah >/dev/null ) 2>&1 | awk -F. '{print $1}')

where you are redirecting the standard error to match the standard output. bash is writing its trace-messages to the standard error, and is (for instance) using its built-in echo along with other shell constructs all in the bash process.

If you change it to something like

TIMESEC=$(echo blah | sh -c "( /usr/bin/time -f %e grep blah >/dev/null )" 2>&1 | awk -F. '{print $1}')

it will work around that problem, and perhaps be an acceptable compromise between tracing and working:

++ awk -F. '{print $1}'
++ sh -c '( /usr/bin/time -f %e grep blah >/dev/null )'
++ echo blah
+ TIMESEC=0                 
+ echo ABC--0--DEF
ABC--0--DEF
+ '[' 0 -eq 0 ']'
+ echo 'we are here!'
we are here!

Best Answer

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