Chapter 9 - Writing Scripts, Configuring Email and Using Databases Flashcards
Explain the function of environment variables
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Environment variables are used to store information on the system for the benefit of running programs. Examples include the PATH environment variable, which holds the locations of executable programs and HOSTNAME which hols the system’s hostname.
Describe various shell script components
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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 it is a script and indicate the shell interpreter to use. Each script component has a specific syntax needed for proper shell execution and logic flow. A shell script is run using various methods. Each method may or may not create a subshell and may not require the execution bit to be set.
Describe the purpose of shell aliases
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Aliases enable you to create a command “shortcut” a simple command that can stand in for a different or longer command. Aliases are typically defined in 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-remember version of a command.
Summarize the major SMTP servers for Linux
Sendmail was the most common SMTP server a decade ago and it is still very popular today. Postfix and Excim are often supplied as the default mail servers on modern distributions, whereas administrators sometimes install qmail. Postfix and qmail use modular designs, whereas sendmail and Exim do not.
Explain the difference between an email alias and email forwarding
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An email alias is configured system-wide, typically in /etc/alias. it can set up forwarding for any local address, even if the address doesn’t correspond to a real account and if the system is properly configured, only root may edit /etc/aliases and therefore modify aliases. Email forwarding, on the hand, is handled bu the ~/.forward file in a user’s home directory; it is intended as a means for users to control their own email forwarding without bothering the system administrator.
summarize the structure of an SQL database
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Each SQL installation consist of a number of named database, each of which in turn may contain multiple tables. Each table can be thought of as a two-dimensional array of data. Each row in a table describes some object or concept (inventory items, employees, movies in a personal DVD collection and so on) and each column in a table holds data about these objects or concepts (model number, salary or directory)
Describe the commands used to enter data in a SQL database.
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The INSERT command inserts a single entry into a database. It requires a table name and a set of values, as in INSERT, INTO movies 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(s) to be modified.
Explain the commands used to extract data from SQL database
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The SELECT command retrieves data from a SQL database. It can be used with a variety of additional options, such as FROM, JOIN and WHERE, to identify the table(s) from which data should be retrieved and to locate specific values of interest
