以下是man history顯示的信息
history [n]
history -c
history -d offset
history -anrw [filename]
history -p arg [arg ...]
history -s arg [arg ...]
With no options, display the command history list with line numbers. Lines listed with a * have been modified. An argument of n lists only the last n lines. If the shell variable HISTTIMEFORMAT is set and not null, it is used as a format string for strf time(3) to display the time stamp associated with each displayed history entry. No intervening blank is printed between the formatted time stamp and the history line. If filename is supplied, it is used as the name of the history file; if not, the value of HISTFILE is used. Options, if supplied, have the following meanings:
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-c Clear the history list by deleting all the entries.
-d offset
Delete the history entry at position offset.
-a Append the ``new'' history lines (history lines entered since the beginning of the current bash session) to the history file.
-n Read the history lines not already read from the history file into the current history list. These are lines appended to the history file since the beginning of the current bash session.
-r Read the contents of the history file and use them as the current history.
-w Write the current history to the history file, overwriting the history file's contents.
-p Perform history substitution on the following args and display the result on the standard output. Does not store the results in the history list. Each arg must be quoted to disable normal history expansion.
-s Store the args in the history list as a single entry. The last command in the history list is removed before the args are added.
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If the HISTTIMEFORMAT variable is set, the time stamp information associated with each history entry is written to the history file, marked with the history comment character. When the history file is read, lines beginning with the history comment character followed immediately by a digit are interpreted as timestamps for the previous history line. The return value is 0 unless an invalid option is encountered, an error occurs while reading or writing the history file, an invalid offset is supplied as an argument to -d, or the history expansion supplied as an argument to -p fails.
通過上面的man page信息大家可能會看到裡面有一個叫HISTTIMEFORMAT的變量，大家可能都知道history這個命令是顯示歷史命令的，但是如果我想知道你用系統上的那個用戶操作了我這台機器，什麼時間操作的，我們直接用history命令是不可能實現的，那麼下面我們就來看一下如何實現這個功能呢。
其實該變量可以自定義history是的輸出顯示，格式同strftime，可以根據date命令的格式進行設置
[root@ www.linuxidc.com ~]# export HISTTIMEFORMAT="`whoami` : %F %T :"
2333 root : 2012-05-30 13:55:55 :man date
2334 root : 2012-05-30 14:04:49 :cd
2335 root : 2012-05-30 14:04:51 :clear
2336 root : 2012-05-30 14:04:54 :ls
2337 root : 2012-05-30 14:04:58 :history
2338 root : 2012-05-30 14:05:08 :ls
2339 root : 2012-05-30 14:05:16 :vim .bash_profile
2340 root : 2012-05-30 14:05:31 :export HISTTIMEFORMAT="`whoami` : %F %T :"
2341 root : 2012-05-30 14:05:35 :history
如果大家想讓這個變量永久生效的話，可以把export HISTTIMEFORMAT="`whoami` : %F %T : "寫入到~/.bash_profile中，這樣的話就可以永久生效了，不訪大家試試看吧！