Term
| What is the basic function of the BASH shell? |
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Definition
| Providing a user interface and interpreting commands entered on the command line. |
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Term
| What is a file descriptor? |
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Definition
| Command input and output are represented by numeric labels known as file descriptors. |
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Term
| What are three file descriptors? |
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Definition
-Standard input (Stdin)
-Standard output (Stdout)
-Standard error (Stderr) |
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Term
| What is the standard output and in what form does it often take? |
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Definition
| Refers to the normal output of a command. Stdout is displayed on the terminal screen by default. |
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Term
| What is the standard input and in what form does it often take? |
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Definition
| Refers to information processed by the command during execution; this often takes the form of user input typed on the keyboard. |
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Term
| What is the standard error and in what form does it often taken? |
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Definition
| Refers to any error messages generated by the command. Stderr is displayed on the terminal screen by default. |
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Term
| What numbers are used to represent the three file descriptors? |
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Definition
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Term
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Definition
| It means capturing the output from a file, command, program, script, or even code block within a script and sending it as input to another file, command, program, or script. |
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Term
| What is the redirection character and how is it used? |
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Definition
| It is used to send the output from a command to a text file. |
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Term
| If the output of a command is redirected to a currently non-existent file, what will happen? |
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Definition
| The file is automatically created. |
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Term
| If the output of a command is redirected to a currently existing file, what will happen? |
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Definition
| The BASH shell clears it contents before executing the command. |
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Term
| What kind of output can be redirected into a file? |
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Definition
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Term
| If a command specifies that only the standard output be redirected to a file, but there is an error, where will the standard error output be sent? |
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Definition
| The (stderr)is directed to a file called badoutput. |
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Term
| In the absence of a numeric file descriptor, what kind of file descriptor will the BASH shell assume? |
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Definition
| BASH shell assumes stdout. |
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Term
| Can you redirect standard output and standard error to separate files in the same command? |
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Definition
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Term
| Does the order of redirection on the command line matter? |
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Definition
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Term
| Can you use the same filename for both stdout and stderrusing the normal syntax? Why or why not? |
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Definition
| No because using the same file name for both cause a loss of data. |
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Term
| How can you redirect both stdout and stderr to the same file without any loss of data? |
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Definition
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Term
| How do you prevent an existing file's content from bein cleared by the BASH shell, and also tell the shell to append newer output to the output already existing in the file? |
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Definition
| Append output to the existing output, you can specify two > shell metacharacters along side the file descriptor. |
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Term
| How can you redirect a file to the stdin of a command? Do you need to specify the file desciptor number in the command? |
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Definition
| Use the < shell metacharacter because there is only one file descriptor for input, there is no need to specify the number 0 before the < shell metacharacter to indicate stdin. |
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Term
| When combining stdin and stdout, will the BASH shell clear the content of an existing target file before or after manipulating the original file? |
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Definition
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Term
| What is a common command used to clear the content of a file? |
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Definition
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Term
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Definition
| Sending the stdout of one command to another command as stdin. |
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Term
| Does the command 1>file do the same thing as >file? |
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Definition
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Term
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Definition
| String of metacharacters connected by "1" metacharacters. Commonly used to reduce the amount of information displayed on the terminal screen. |
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Term
| Are spaces required around the pipe shell metacharacter? |
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Definition
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Term
| What is one common use for piping? |
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Definition
| To reduce the amount of information displayed on the terminal screen from commands that display too much information. |
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Term
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Definition
| Any command that can take stdin and transform it in to stdout. |
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Term
| Where must commands that are not filter commands be in a pipe? |
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Definition
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Term
| Why can't interactive commands (like vi)be used between two pipe symbols? |
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Definition
| They cannot take from stdin and give to stdout. |
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Term
| What filter command takes information from stdin and sends that information to a file, as well as to stdout. |
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Definition
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Term
| If you combine redirection and piping, where must you place input and output direction? |
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Definition
| Input direction occurs at the beginning of the pipe and output direction occurs at the end of the pipe. |
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Term
| What command is typically used to search for a certain string of text, and replaces that text string with another text string? What is this command's syntax for both finding only the first occurrence and for all occurrences? |
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Definition
-sed command
-sed s/search/replace/
-sed s/search/replace/g |
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Term
| What other command searches for patterns of text, but treats each line of text as a record in a database, and each word in a line as a database field? |
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Definition
-awk command
Example:
cat prologue | awk '/the/{print$1,$4}' |
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Term
| By default, what does the awk command use as delimeters for each field in a line? How can you change the delimeter? |
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Definition
Use spaces or tab characters
-F option |
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Term
| Can sed and awk use regular expressions? |
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Definition
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Term
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Definition
| A reserved portion of memory containing information that might be accessed. |
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Term
| What are environment variables? |
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Definition
| They are typically set by the system and contain information that the system and programs access regulary. |
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Term
| Can users create their own variables? |
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Definition
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Term
| What are special variables? |
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Definition
| They can only be referenced and never directly assigned values. |
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Term
| What command is used to see a list of environment variables? |
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Definition
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Term
What do the following variables define?
-SHELL
-PS1
-HOME
-PWD
-PATH |
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Definition
-SHELL:pathname to shell
-PS1:the default shell prompt
-Home:the absolute pathname to the user's homew directory.
-PWD:the present working directory in the directory tree
-Path:a list of directories to search for executable programs. |
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Term
| How do you view the content of a variable? What does the $ character do? |
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Definition
| Use the echo command and specify the variable name prefixed by the $ shell metacharacter. |
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Term
| How do you change a variable name? |
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Definition
| Specify the variable name followed immediately by an equal siqn(=) and the new value. |
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Term
| What are some variables whose values should not be changed? |
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Definition
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Term
| What exactly does the tilde(~) metacharacter represent? |
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Definition
| Represents the current user's home directory. |
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Term
| Why is PATH variable so important? |
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Definition
| Allows users to execute commands by typing the command name alone. |
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Term
| What must you do to run an executable whose location is not listed by the PATH variable? |
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Definition
| The user must specify either the absolute or relative pathname to the executable file. |
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Term
| How do you define a use variable? |
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Definition
| Specify the name of the variable(variable identifier)immediately followed by the equal sign(=) and the new contents. |
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Term
| What are the rules for creating user defined variables? |
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Definition
-They contain alphanumeric characters(0-9, A-Z, a-z, the -(dash) character, or the _(underscore) character.
-They must not start with a number
-They are typically capitalized to follow convention(for example, Home, Path, and so on). |
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Term
| When you execute a command in the current shell, usally where is the command run? |
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Definition
| They are run in separate subshell, which is created by the current shell. |
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Term
| Are variables created in the current shell available to subshells? |
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Definition
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Term
| What command is used to export variables to ensure that all programs started by the current shell have the ability to access the variable? |
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Definition
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Term
| What command other than set can be used to see a list of all exported environment and user defined variables in the shell? |
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Definition
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Term
| What are some examples of other variables that perform special functions? |
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Definition
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Term
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Definition
| Aliases are shortcuts to commands stored in special variables that can be created and viewed using the alias command. |
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Term
| How do you create aliases to multiple commands? |
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Definition
| They are separated by the ; shell metacharacter. |
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Term
| Is it necessary to use unique alias names? |
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Definition
| Yes because the shell searches for them before it searches for executables files. |
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Term
| What are environment files? Why are they important to variables? |
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Definition
| To ensure that variables are accessible to a shell at all times, you must place variables in a file that is executed each time a user logs in and starts a BASH shell. |
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Term
| What is the ~/.bashrc file and what does it do? |
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Definition
| (BASH run-time configuration) is typically used to set aliases and variables that must be present in the BASH shell. |
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Term
| Which environment file sets HOME and PATH environment variables? |
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Definition
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Term
| How do you add a variable to an environment file? |
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Definition
| Add a line that has the same format as the command used on the command line. |
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Term
| What else can be placed within an environment file beside variables? |
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Definition
| Any command that can be executed on the command line. |
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Term
| In which file would you add clean up commands (such as archive log files)so that they run upon exiting the shell? |
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Definition
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Term
| What are shell scripts? For what are they typically used? |
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Definition
-Text files containing commands and special constructs.
-To create custom programs that perform adminstrative tasks on Linux systems. |
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Term
| What commands can be used in shell scripts? |
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Definition
| Any command that can be entered on the command line in Linux. |
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Term
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Definition
| The first line in the preceding shell script(#!/bin/bash) |
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Term
| What character in a shell script identifies the line as a comment? |
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Definition
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Term
| How do you execute a shell script if you only have read permission for that script? |
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Definition
| By starting another BASH shell and specifying the shell script as an argument. |
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Term
| How do you execute a shell script if you have read and execute permissions? |
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Definition
| You can execute the shell script like any other executable program on the system. |
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Term
| What command can be utilized in a script to improve readability via the use of blank lines? |
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Definition
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Term
| What are escape sequences? How are they used? |
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Definition
Special notations
Example:
echo -e"Today's date is: \c"
date |
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Term
| What command takes user input from stdin and places it in a variable specified by an argument to the read command? |
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Definition
read command
Example:
echo -e"What is your name? -->\c"
read USERNAME |
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Term
| What are decision constructs? |
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Definition
| They are the most common type of construct used in shell scripts. |
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Term
| What is the basic syntax of the if construct? |
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Definition
if this true
then
do these commands
elif this is true
then
do these commands
else
do these commands
fi |
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Term
| What character end an if construct? |
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Definition
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Term
| What are the six common rules that govern if constructs? |
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Definition
-elif and else statements are optional
-you can have an unlimited number of elif statements
-the "do these commands" section can consist of multiple commands
-the "do these commands" section is typically indented per line from the left-hand side of the text file.
-the end statement must be a backward "if"(fi).
-the this is true part of the if syntax, can be a command or test statement. |
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Term
| Can you use the "if" construct to alter the flow of the program given input from the user? |
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Definition
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Term
| What must you include after the beginning square bracket and before the ending square bracket in a test statement? |
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Definition
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Term
| Compare to the "if" construct, why use the "case" construct? |
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Definition
| Whe presenting several choices, it is common place to use a case construct. |
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Term
| What is the syntax of the case construct? |
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Definition
case variavle in
patter1 )do this
;;
pattern2 )do this
;;
pattern3 )do this
;; |
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Term
| How does the "case" construct work? |
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Definition
| Compares the value of a variable with several different patterns of text or numbers. |
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Term
| What does the && construct do? What is its syntax? |
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Definition
The command on the right of the && construct is executed only if the command on the left of && construct completed successfully.
-command && command |
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Term
What does the || construct do?
What is the syntax? |
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Definition
the command on the right of the || construct is executed only if the command on the left of the || construct did not complete successfully.
-command || command |
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Term
| For what is the "loop" construct used? How do they work? |
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Definition
Execute commands repetitively.
-alters the flow of a program based on the result of a particular statement. |
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Term
| What are the two most common loop constructs? |
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Definition
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Term
| What is the syntax of the "for" construct? |
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Definition
for var_name in string1 string2 string3 ... ...
do
these commands
done |
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Term
| What is the "while" construct? What is the syntax of the "while" construct? |
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Definition
-Common loop construct used within shell scripts.
while this returns true
do
these commands
done |
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Term
| What is a counter variable, and what does it do? |
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Definition
| Counter variable whose values changes each time through a loop. |
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Term
| What can you use in place of a test statement to create a "while" construct that executes indefinitely? |
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Definition
| you can use the true or : |
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