In the following example pwd was typed three times, when you do history, you can see all the 3 continuous occurrences of it. To eliminate duplicates, set HISTCONTROL to ignoredups as shown below.
# pwd # pwd # pwd # history | tail -4 44 pwd 45 pwd 46 pwd 47 history | tail -4
Note: There are three pwd commands in history, after executing pwd 3 times as shown above
# export HISTCONTROL=ignoredups # pwd # pwd # pwd # history | tail -3 56 export HISTCONTROL=ignoredups 57 pwd 58 history | tail -4
Note: There is only one pwd command in the history, even after executing pwd 3 times as shown above