10 Shell and environment variables

Question 1

Set variable to value:

Answer 1

variable=value

Question 2

Make variable visible to called programs:

Answer 2

export variable

export variable=value

Question 3

Modify environment variables for one command only:

Answer 3

variable1=value variable2=value command

Question 4

shows all shell variables

Answer 4

set

Question 5

shows all (exported) environment variables.

Answer 5

printenv

Question 6

home directory

Answer 6

$HOME

~

Question 7

Your login name.

Answer 7

$USER/$LOGNAME

Question 8

Colon-separated list of directories in which shell looks for commands (e.g., “/bin:/usr/bin:/usr/X11R6/bin”).
Should never contain “.”, at least not at beginning. Why?

Answer 8

$PATH

Question 9

Colon-separated list of directories where the loader looks for shared libraries (see man ld.so)

Answer 9

$LD_LIBRARY_PATH

.. C security issue

Question 10

Locale

Answer 10

$LANG, $LC_*

Your “locale”, the name of a system-wide configuration file with information about your character set and language/country conventions (e.g., “en_GB.UTF-8”). $LC_* sets locale only for one category, e.g. $LC_CTYPE for character set and $LC_COLLATE for sorting order; $LANG sets default for everything. “locale -a” lists all available locales.

Question 11

Specification of your timezone (mainly for remote users)

Answer 11

$TZ

Question 12

Previous working directory, also available as “~-”

Answer 12

$OLDPWD

Question 13

Change the command prompt

Answer 13

$PS1 — The normal command prompt, e.g.

$ PS1=’[\033[7m]\u@\h:\W !$[\033[m] ‘

Question 14

Printers

Answer 14

$PRINTER — The default printer for lpr, lpq and lprm.

Question 15

Terminal type

Answer 15

$TERM — The terminal type (usually xterm or vt100).

Question 16

Pager/editor

Answer 16

$PAGER/$EDITOR — The default pager/editor (usually less and emacs, respectively).

Question 17

X server that clients shall use

Answer 17

X server - the program that has control over the screen

$DISPLAY

Question 18

environment variables documentation

Answer 18

man 7 environ