You’d like more control over your command-line history.

Set the $HIST* variables and shell options as desired.

The $HISTFILESIZE variable sets the number of lines permitted in the $HISTFILE. The default for $HISTSIZE is 500 lines, and $HISTFILE is ~/.bash_history unless you are in POSIX mode, in which case it’s ~/.sh_history. Increasing $HISTSIZE may be useful, and unsetting it causes the $HISTFILE length to be unlimited. Changing $HISTFILE probably isn’t necessary, except that if it is not set or the file is not writable, no history will be written to disk. The $HISTSIZE variable sets the number of lines permitted in the history stack in memory.

$HISTIGNORE and $HISTCONTROL control what goes into your history in the first place. $HISTIGNORE is more flexible since it allows you to specify patterns to decide what command lines to save to the history. $HISTCONTROL is more limited in that it sup-ports only the few keywords listed here (any other value is ignored):

If $HISTCONTROL is not set, or does not contain any of these keywords, all commands are saved to the history list, subject to processing $HISTIGNORE. The second and subsequent lines of a multiline compound command are not tested, and are added to the history regardless of the value of $HISTCONTROL.

(Material in the preceding paragraphs has been adapted from Edition 2.5b of The GNU Bash Reference Manual for bash Version 2.05b, last updated July 15, 2002; http://www.gnu.org/software/bash/manual/bashref.html.)

As of bash version 3, there is a fascinating new variable called $HISTTIMEFORMAT. If set and non-null, it specifies an strftime format string to use when displaying or writing the history. If you don’t have bash version 3, but you do use a terminal with a scroll-back buffer, adding a date and time stamp to your prompt can also be very helpful. See Customizing Your Prompt. Watch out because stock bash does not put a trailing space after the format, but some systems (e.g., Debian) have patched it to do so:

bash-3.00# history
    1  ls -la
    2  help history
    3  help fc
    4  history

# Ugly
bash-3.00# export HISTTIMEFORMAT='%Y-%m-%d_%H:%M:%S'

bash-3.00# history
    1  2006-10-25_20:48:04ls -la
    2  2006-10-25_20:48:11help history
    3  2006-10-25_20:48:14help fc
    4  2006-10-25_20:48:18history
    5  2006-10-25_20:48:39export HISTTIMEFORMAT='%Y-%m-%d_%H:%M:%S'
    6  2006-10-25_20:48:41history

# Better
bash-3.00# HISTTIMEFORMAT='%Y-%m-%d_%H:%M:%S; '

bash-3.00# history
    1  2006-10-25_20:48:04; ls -la
    2  2006-10-25_20:48:11; help history
    3  2006-10-25_20:48:14; help fc
    4  2006-10-25_20:48:18; history
    5  2006-10-25_20:48:39; export HISTTIMEFORMAT='%Y-%m-%d_%H:%M:%S'
    6  2006-10-25_20:48:41; history
    7  2006-10-25_20:48:47; HISTTIMEFORMAT='%Y-%m-%d_%H:%M:%S; '
    8  2006-10-25_20:48:48; history

# Getting tricky now
bash-3.00# HISTTIMEFORMAT=': %Y-%m-%d_%H:%M:%S; '

bash-3.00# history
    1  : 2006-10-25_20:48:04; ls -la
    2  : 2006-10-25_20:48:11; help history
    3  : 2006-10-25_20:48:14; help fc
    4  : 2006-10-25_20:48:18; history
    5  : 2006-10-25_20:48:39; export HISTTIMEFORMAT='%Y-%m-%d_%H:%M:%S'
    6  : 2006-10-25_20:48:41; history
    7  : 2006-10-25_20:48:47; HISTTIMEFORMAT='%Y-%m-%d_%H:%M:%S; '
    8  : 2006-10-25_20:48:48; history

The last example uses the : built-in with the ; metacharacter to encapsulate the date stamp into a “do nothing” command (e.g., : 2006-10-25_20:48:48;). This allows you to reuse a literal line from the history file without having to bother parsing out the date stamp. Note the space after the : is required.

There are also shell options to configure history-file handling. If histappend is set, the shell appends to the history file; otherwise it overwrites the history file. Note that it is still truncated to $HISTSIZE. If cmdhist is set, multiline commands are saved as a single line, with semicolons added as needed. If lithist is set, multiline commands are saved with embedded newlines.