.. default-role:: literal


Bash tips and tricks
====================

Concatenate two arrays
----------------------

Let's say I have two arrays::

    myarray1=( '1' '2' '3' )
    myarray2=( '4' '5' '6' )

what I want is to get a third array containing the content of the first array
and the content of the second one. This is the equivalent of `python's extend
function`_. The syntax to do this is (as often in bash) horrible::

    myarray3=( ${myarray1[@]} ${myarray2[@]} )

To test that it worked::

    echo ${myarray3[@]}

The `Linux documentation project`_ has a nice page on `bash arrays`_

.. _python's extend function: http://docs.python.org/library/stdtypes.html#mutable-sequence-types
.. _Linux documentation project: http://tldp.org/
.. _bash arrays: http://tldp.org/LDP/abs/html/arrays.html

Change history settings
-----------------------

Set the number of commands remembered
#####################################

To make sure bash does not remembers everything you type, you should set the
exact number of commands you want to be remembered. This is described by the
`HISTSIZE` environment variable. For example, to set the size to 20, put the
following line in your `.bashrc`::

    export HISTSIZE=20

You can also set the number of lines in your history file (`.bash_history` by
default) using the `HISTFILESIZE` variable.

Make bash forget some commands
##############################

You can make bash not log some commands using the `HISTIGNORE` variable. It
contains a comma-separated list of patterns that should be ignored. 

A nice trick is to ignore all commands beginning with a space::

    export HISTIGNORE='[ ]*'

This way when I do not want bash to log a given command, I just preceed it by a
space.

References
----------

* `Using Bash's History Effectively`_  is a nice tutorial on bash's command
  history.

.. _Using Bash's History Effectively: http://www.talug.org/events/20030709/cmdline_history.html