Chapter 9 Flashcards
Using a semicolon allows you to do what?
command ; command
Combine two commands into one line
known as the list operator
455
subshell
a child process that is created by either the shell or a shell script when a process is initiated
454
Variable
DISPLAY
identifies the display. Usually set to :0.0, which indicates the first display on the current computer. If running multiple sessions the counter increases to ID it. :0.0 is the first one, :1.0 is the second, etc
456
Variable
EDITOR
Some programs launch the program pointed to by the environment variable when they need to call a text editor for you to use.
456
Variable
HISTSIZE
This variable determines the number of commands that will be saved in your history file
456
Variable
HOME
Points to your home directory. Some programs use it to help them look for configuration files or as a default locations in which to store files
456
Variable
HOSTNAME
This is the current TCP/IP hostname of the computer
456
Variable
LANG
The system holds your current language, specified locale, using this.
456
Variable
LD_LIBRARY_PATH
A few programs use this environment variable to indicate directories in which library files may be found. It works much like a path
456
Variable
LOGNAME
This variable holds your username when you are logged into the systems
456
Variable
This variable holds the location of the user’s mail spool. It’s usually /var/spool/mail/username
456
Variable
PAGER
If set, this variable determines the pager to use for output by programs, such as man
456
Variable
PATH
This is an unusually important environment variable. It sets the path for a session, which is a colon-delimited list of directories
457
Variable
PS1
This is the default prompt in bash. It generally includes variables of its own, such as \u (username) \h (hostname), and \W (for profile)
457
Variable
PWD
This is the present working directory. This environment variable is maintained by the system. Programs may use it to search for files when you don’t provide a complete pathname
457
Variable
SHELL
holds the path to the current command shell
457
Variable
TERM
name of the current terminal type. To move display of text effects for programs like text-mode editors
457
Variable
TZ
Sets the environment variable to your own timezone which is most useful if that’s different than the computer’s time zone
457
Variable
USER
Current username. It’s a variable that’s maintained by the system
457
Variable
USERNAME
An alternative to the USER variable
457
Conditional Expression
enables a script to determine whether to follow a script based on a qualifier
478
user-defined variable
variable defined by a user for various purposes like storing data
474
writing a condition
use [ condition ]
the spaces are necessary! Linux is stupid!
482
elif
means “else if”
483
||
means or
483
For loop syntax
For variable in list
do
commands
done
490
sendmail
former dominant program for sending email server packages on the Internet. Still very powerful
499
Postfix
modular replacement for sendmail. Sendmail uses a single program to do everything, postfix uses multiple programs, each with its own specific small task
499
Exim
Like sendmail, but with a simpler configuration file format making it easier to configure
499
Qmail
4th major Linux email server. Modular server with security as a major design goal.
499
mail server options
-v
produces a verbose output. Helpful when debugging
501
mail server options
-s
subject option enables you to specify the subject line
501
mail server options
-f
to read your email.
501
Environmental Variables
means to pass names and data. Used to store information on the system for the benefit of running programs. There are over 40 default in the system.
515
