Wednesday, 10 September 2014

Tips & Tuning history file.

7 Tips that can help you to improve you Bash history file.
You will learn how to add date and time to bash history file, increase history size, ignore specific commands and much more ..

1. Add Date and Time to Bash History

Sometimes it would be very nice to know when some command got executed.
Set HISTTIMEFORMAT to print the time stamps associated with each history entry.
Append the following line to ~/.bashrc file :

 export HISTTIMEFORMAT="%h %d %H:%M:%S "

Now, when you type history, it will show something like :

113  Jun 08 16:31:06 sudo ifconfig
114  Jun 08 16:31:10 top
115  Jun 08 16:31:19 ping
116  Jun 08 16:31:22 history

2. Increase Bash History Size

Increase HISTSIZE - the number of commands to remember in the command history (the default value is 500).
export HISTSIZE=10000

Increase HISTFILESIZE - the maximum number of lines contained in the history file (the default value is 500).
export HISTFILESIZE=10000


 3. Append Bash Commands to History File

Bash overwrites .bash_history file?

shopt -s histappend

4. Store Bash History Immediately

By default, Bash only records a session to the .bash_history file when the session terminates.
This means that if you crash or your session terminates improperly, you lose the history up to that point.
Use $PROMPT_COMMAND variable to save each command right after it has been executed.
Append the following line to ~/.bashrc file, if the variable $PROMPT_COMMAND hasn't been set yet :
PROMPT_COMMAND='history -a'

Append the following line, if the variable $PROMPT_COMMAND has already been set :



5. Control Bash History

HISTCONTROL is a colon-separated list of values controlling how commands are saved in the history file.
Value Description
ignorespace don't save lines which begin with a <space> character
ignoredups don't save lines matching the previous history entry
ignoreboth use both 'ignorespace' and 'ignoredups'
erasedups eliminate duplicates across the whole history
Example :
export HISTCONTROL=ignorespace:erasedups



6. Ignore Specific Commands

HISTIGNORE is a colon-separated list of patterns used to decide which command lines should be saved in the history file.
Don't save ls, ps and history commands :
export HISTIGNORE="ls:ps:history" 

 Don't save commands with s in the beginig :

export HISTIGNORE="s*"



7. Use one command per line

Store multi-line commands in one history entry :
shopt -s cmdhist


 Change the History File Name

Use HISTFILE to change the name of the file in which Bash history is saved. The default value is ~/.bash_history.
export HISTFILE=~/.custom_file

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