Bash environment

more infos at http://doc.ubuntu-fr.org/variables_d_environnement

Assign values to environment variables

To assign a value to an existing environment variable, we use an assignment expression. For example, to assign the "en_US.UTF-8" value to the variable "LANG", we use the following command:

LANG=fr_FR.UTF-8

If we use an assignment expression to a variable that does not exist, the shell will create a "shell variable", which is similar to an environment variable, but that will not affect the behavior of other applications.

A shell variable can be exported to become an environment variable with the export command. To create the environment variable "EDITOR" and assign the value "nano", several methods can be used. Here's one we propose:

EDITOR=nano
export EDITOR

The bash shell (the one that comes by default with Ubuntu) provides a shortcut for creating environment variables. The previous example can be condensed into a single command line:

export EDITOR=nano

Examine the values of environment variables

The printenv command displays the names and values of all environment variables set:

printenv 

To examine the value of a particular variable, simply specify its name after the printenv command:

printenv TERM

The variable's value can be retrieved using the "$" sign in front of his name, as in the following example:

echo $TERM

There is a command to make temporary changes in the short term, on the environment. This can also be used to display the current environment variables. This is the env command:

env

The dollar sign can be used to retrieve the value of environment variables in command lines. For example, the following command can be used to list the desktop files (Desktop folder) of the current user:

ls $HOME/Desktop

Clear environment variables In most cases, assign an empty value for an environment variable enough to cancel its effect, as in the example below. However, some variables such as "POSIXLY_CORRECT" influence the programs of their very existence, even if their value is empty.

export LC_ALL=

The unset command can be used to completely remove an environment variable:

unset LC_ALL

It is also possible to use the export command with the -n argument. This will result in losing the variable sound environment variable status, it becomes a shell variable while retaining its value.

export -n LC_ALL

main variables of environment

User Environment

Variable	Example value	Role
USERNAME	user_name	The user name currently connected. This variable is defined by the système.Vous certainly should not change its value manually.
LOGNAME	user_name	Similar to USER, some programs use it in preference to USER
HOME	/home/utilisateur	Location user's home directory currently connected.
PWD	/home/utilisateur/Desktop	The current working directory of the shell.
SHELL	/bin/bash	The preferred shell as the user that is defined in the "/ etc / passwd"
POSIXLY_CORRECT	s.o.	The very existence of this environment variable, regardless of its value, forcing some utilities to behave in a manner more consistent with the POSIX standard. This can cause dysfunction of various GNU tools that make life easier, but it may be just what is sought to properly operate old UNIX scripts.
HOSTALIASES	/etc/host.aliases	The file name containing guest alias names for use with a variety of network software.
TZDIR	/usr/share/zoneinfo	The path of the folder containing the information on time zones files (TimeZoneDIRectory) .It is usually no need to manually set as systems seek such files in / usr / share / zoneinfo, by default.
TZ	IST-2:Japan	This variable was used by the ancient Unix systems to specify the time zone of the system. However, Ubuntu and most newer systems use for that / etc / localtime. It can be used to néamoins a particular user session displays the time in a different time zone from that of the system. The value of this variable can be either the name and offset from one time zone (first example) or the name of a zone file located in / usr / share / zoneinfo (second example).
TERM	xterm	The name of the terminal on information files located in / lib / terminfo, this file tells the program in console mode how to perform tasks such as color display. It may be useful to play with this variable if you try to use an unusual terminal emulation program, or if you try to connect a terminal emulator hardware via serial port and you do not get the desired results.
TERMCAP		This variable can be used instead of "TERM" to specify the information on the device manually, instead of using a file.
COLUMNS	80	The number of columns on the console window. Try adjusting this variable if lines do not wrap sccm to juste in the console.
LINES	25	The number of lines in the console window. Try adjusting this variable if you get strange results when you scroll the text.
http_proxy	http://user:passwd@proxy:port/	The variable to use a proxy, also works with HTTP_PROXY, ftp_proxy and FTP_PROXY

Regional Environment

Variable	Role
$LANG	The basic language setting used by system applications, as long as it is not contradicted by another variable
$LC_CTYPE	The character set used to enter and display text
$LC_NUMERIC	Formatting non-monetary numeric values
$LC_TIME	Format for date and time
$LC_COLLATE	How to sort various information such sets alphabetical order so that the items can be sorted alphabetically using the sort command
$LC_MONETARY	Format monetary numeric values
$LC_MESSAGES	Language used to display messages to the user
$LC_PAPER	Definitions of standard paper sizes
$LC_NAME	Format names
$LC_ADDRESS	Addresses Format
$LC_TELEPHONE	Structure of telephone numbers
$LC_MEASUREMENT	Measurement units to use
$LC_IDENTIFICATION
$LC_ALL	This variable has a powerful role to crush the other locales. When a value is assigned, applications use this value regardless of the values of other variables