Chapter 9 Writing Scripts, Config Email and using Databases

Question 1

Display

Answer 1

This variable identifies the display used by the X windows server. It’s usually set to :0.0, which indicates the first display on the current computer. You ccan run Multiple X Sessions on one computer in which case each one gets a different DISPLAY number- for instance, :0.0 for the first session and :1.0 for the second session.

Question 2

Editor

Answer 2

Some programs launch the program pointed to by this enviorment variable when they need to call a text editor for you to use. Thus, changing this variable to your favorite editor can help you work in linux. It’s best to set this variable to a text-mode editor because GUI editors may cause problems if theyre called from a program that was launched from a text mode.

Question 3

This varible determines the number of commands that will be saved in your history file.

Answer 3

HISTSIZE

Question 4

This variable points to your home directory. Some programs use it to help them look for configuration files or as a default location in which to store files.

Answer 4

HOME

Question 5

This is the current TCP/IP hostname of the computer.

Answer 5

HOSTNAME

Question 6

A Few programs use this environment variable to indicate directories in which library files may be found. It works much like PATH

Answer 6

LD_LIBRARY_PATH

Question 7

The system holds your current language, specified as a locale,using this variable. Locales are describes further in Ch 6 “config the X Windows Systems, Localization and Printing”

Answer 7

LANG

Question 8

This variable holds your username when you are logged into the system.

Answer 8

LOGNAME

Question 9

This variable holds the location of the user’s mail spool. It usually /var/spool/mail/username

Answer 9

MAIL

Question 10

If set, this variable determines the pager to use for output by programs, such as man

Answer 10

PAGER

Question 11

This is the default prompt in bash. It generally includes. It generally includes variables of its own, such as \u (for the username), \h (for the hostname) and \W for the current working directory) This value is frequently set in /etc/profile, but users often over ride it.

Answer 11

PS1

Question 12

This is the present working directory. The enviorment variable is maintained by the system. Programs may use it to search for files when you dont provide a complete pathname.

Answer 12

PWD

Question 13

The variable holds the path to the current command shell.

Answer 13

SHELL

Question 14

You can set this enviorment variable to your own time zone, which is the most useful if thats different than they computers time zone- for instance, if your using a computer remotely.

Answer 14

TZ

Question 15

User or Username

Answer 15

This is your current username. Its variable thats maintained by the system.

Question 16

is parameter is what you want to type at the command prompt, and the shell substitues command for whatever you type.

Answer 16

alias_name

Question 17

Vocab

is a variable defined by a user for various pruposes, such as temporarily storing data.

Answer 17

user defined variable

Question 18

Explain the function of enviorment variables

Answer 18

Enviorment variables are used to store information on the systems for the benefitws of running programs. Examples include the pathenviorment variable, which holds the locations of executable programs and HOSTNAME which holds the systems hostname.

Question 19

Describe various shell script components?

Answer 19

A shell script combines several commands, possibly including conditional expressions, variables, and other programming features. A shell script must start with a shebang line to let the kernel know its a script and indicate the shell interperter to use. Each script component has a specific syntax needed for proper shell execution and logic flow. A shell script is run using vatious methods. Each method may or may not create a subshell and may or maynot require the execution bit to be set.

Question 20

Describe the prupose of shell aliases?

Answer 20

aliases enable you to create a command “shortcut” a simple command that can stand in for different or longer command. Aliases are typically defined in a shell startup scripts as a way to create a shortened version of a command. aliases also allow useful command options to be used as the new default or they create an easier to remeber verstion of a command.

Question 21

Summarize the major SMTP servers for linux

Answer 21

Sendmail was the most common SMTP server a decade ago, and it is still very popular today. Postfix and Exim are often supplied as the default mail servers on modern distributors, whereas administrators soetimes install qmail. Postfix and qmail use modular designs,whereas sendmail and Exim do not.

Question 22

Summerize the structure of a SQL Database?

Answer 22

Each SQL instllation consists of a numver of naed databases, each of which in turn may contain miltiple tables. Each table can be thought of as two dinensional array of data. Each row in a table describes some object or concept(inventory,employees,movies in a personal DVD collection and so on and each column in a table holds data about these objects or conceptys(model number,salary or director for example.

Question 23

Describe the commands used to enter in a SQL Database?

Answer 23

The INSERT command inserts a single entry into a database. It requires a table name and set values, as in INSERT ITO Moves VALUES(‘Brazil’, “terry Gilliam’, 1985); The update command can be used in a similar way to update an existing entry, but you must use SET to specify the column to set and WHERE to identify the row or rows to be modified.