Bash: Customization Basics

The real power of bash is in its potential for limitless customization. When a bash shell is started, it goes down a list of predefined paths, looking for customization files. Depending on your operating system, it is likely that 99% of what you will need to do can be accomplished in .bash_aliases or .bashrc, which are located in the top-level of your user directory.

Depending on how bash is invoked and initialized, there are a handful of other places it will look for customizations.

(ex: SSH, SU)

1. /etc/profile (global settings)
   1. /etc/profile.d/ (global settings)
2. /etc/bashrc (global settings)
3. ~/.bash_profile (user-only)
   1. ~/.bashrc (user-only)
   2. ~/.bash_aliases (user-only)
4. ~/.bash_logout (user-only, upon logout)

(ex: within X window manager)

1. ~/.bashrc
2. ~/.bash_aliases

(ex: scripts)

1. Defined by BASH_ENV

###### `$ echo $PATH` See directories bash looks for scripts in.

• User specific functions should go in user\'s .bashrc
• Global functions should be individual files in /etc/profile.d/

###### `$ alias -p` See list of active aliases.

###### `$ alias li=\'ls -li\'` Create alias for li for current shell process only.

###### `$ unalias` For unsetting aliases.

###### `$ env` See list of global variables.

###### `$ printenv` Same as above, but with less available option flags.

###### `$ set` See full list of global and local variables.

###### `$ declare` Another long list of environment variables.

###### `$ printenv HOME` See value for global variable HOME.

###### `$ echo $HOME` Same as above.

###### `$ ls $HOME` Use global variable HOME as part of another command.

###### `$ testvar=testvalue` Set value of new local variable \'testvar\'.

###### `$ testvar=\“A String Value\”` Same as above, but for strings.

###### `$ testvar=$testvar:moredata` Append more data to the end of existing variable.

###### `$ testvar=$(other | commands)` Assign variable the result of set of commands.

###### `$ export testvar` Export a local variable to the global environment.

###### `$ unset testvar` Removes variable \'testvar\'.

###### `$ vararray=(one two three four five)` Define multiple values for variable as array.

###### `$ echo ${vararray[2]}` Echo column three from vararray.

###### `$ echo ${vararray[*]}` Echo entire array from vararray.

###### `$ vararray[2]=whatever` Change the value of column three in vararray.

###### `$ unset vararry[2]` Remove column 2 from vararray. Prior col 3 now new col 2.

• Get value of variables with `$`, but don\'t use `$` when assigning them.
• Global environment variables can be accessed from any child shells of the parent from which it was defined.
• Local environment variables can only be accessed from the process in which they were defined.
• Export and unset, when used in a child shell, will not affect the parent shell.
• Variable arrays start with an index value of zero, not one.

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