例如：
$ echo test1 $ echo test2 $ history | tail -n2 1015 echo test1 1016 history | tail -n2
这里是男人bash说：
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 ofignoredupscauses lines matching the prevIoUs history entry to not be saved. A value ofignorebothis shorthand forignorespaceandignoredups. A value oferasedupscauses 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. IfHISTCONTROLis 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 ofHISTIGNORE. The second and subsequent lines of a multi-line compound command are not tested,and are added to the history regardless of the value ofHISTCONTROL.
也可以看看：
> Why is bash not storing commands that start with spaces?在unix SE
> Why does bash have a HISTCONTROL=ignorespace option? at unix SE
