Fox Chapter 9 & 16

Shell

An interpreted environment where commands are entered and executed line by line.

Interpreted program

A program that is translated and executed line by line.

Compiled program

A program that is translated entirely before execution.

Bourne Shell

One of the earliest Unix shells created in 1977.

Bash

A shell that includes features from the Bourne shell and simplifies syntax for user-friendliness.

History list

A record of commands entered in the current Bash session.

Control+p

Command to retrieve the previous instruction from the history list.

Control+n

Command to display the next command from the history list.

Tab completion

A feature that completes directory or filename inputs automatically.

Alias

A shortcut command that represents a longer command in the shell.

Tilde expansion ~

A shorthand for referencing the user's home directory in commands.

Brace expansion {}

Used to create a series of items or commands by enclosing them in braces.

Wildcard

Can act as anything , * “match anything”

Environment variable

A variable defined by the operating system or applications, capitalized.

User variable

A variable defined by the user and used for command-line operations.

echo command

A command that prints text or variable values to the terminal. You can also view the contents of a variable using this command.

Redirection

The process of changing the standard input/output of commands.

Pipe

A method to redirect the output of one command as input to another.

Manual pages

Documentation for commands accessed using the 'man' command.

Text editor

A program used to edit plain text files, e.g., vi and emacs.

Conditional statement

A statement that executes based on whether a specified condition is true.

Iteration

The repetition of a process in programming, exemplified by loops.

While loop

A loop that executes while a given condition remains true.

If-then statement

A control structure that executes actions based on a condition.

Parameter

A value passed to the script or function for processing.

Script

An interpreted program that can accept parameters and has executable code.

Arithmetic operation

Basic math operations performed with numerical inputs in scripts.

exit status

A numerical representation of a command's success or failure, typically `0` for success.

What does typing !number where number is the number of the entry in the history list do?

Recalls an instruction from the history list

control+f

move cursor forward one character

control+b

move cursor backward one character

Escape key+f

move cursor forward one word

escape key+b

move cursor backward one word

control+a

move cursor to the beginning of the line

control+e

move cursor to the end of the line

control+d

delete the character where the cursor is at

control+k

 kill(delete) the contents from the cursor to the end of the line

control+w

delete all the characters before the cursor to the beginning of the word

control+y

take whatever was recently deleted and yank it back put it in current cursor position

control+_

undo the last editing operation (delete or paste) 

(T/F) Bash will treat any number as a string unless you specify that it should be a number

True

How do we change a number to a number and not a string in bash?

Enclose in parantheses

How would we obtain a value stored in a variable?

Add $ before variable name

How would we reference the command date ?

` date `

What does the PATH variable store

 a list of directories, whenever you enter a Linux command or file name, if the item is not found in the current working directory, then the Linux interpreter checks for the item in every directory

How to add to your PATH variable?

PATH=$PATH:/home/nameofdirectory

< redirection

redirect the input to come from an input file

> redirection

redirect the output to go to an output file, overwriting the file if it already exists.

>> redirection

redirect the output to be appended to an already existing file, or create the file if it does not exist

<< redirection

redirect the input to come from keyboard where input will terminate with a special keyword that you specify after

| redirection

redirect the output of one command to be the input of another

Most common form of help; use this command for knowing about an instruction

man command

How does the find command differ from the man command?

Includes list of examples

Apropos

allows us to search for a command based on what it accomplishes/does.

3 common text editors

• GUI editor : Text Editor

• vi

• emacs

3 different modes of vi

command mode, insert mode and replace mode.

Command mode

 is the default mode in vi so keystrokes are interpreted as commands, a command preceded by a number means that command is performed that many times

Insert Mode

 is the mode in vi similar to a word processor, with each keypress the cursor advances to the next position. The only keystroke command in this mode is the escape key, which exits the mode returning you to command mode. 

Replace mode

mode in vi that as you enter keystrokes the characters overwrite the characters already present. 

o (vi text editor mode command)

insert a blank line after the current line and enter insert mode

O (vi text editor mode command)

insert a blank line before the current line and enter insert mode

I (vi text editor mode command)

Enter insert mode at the beginning of current line

A (vi text editor mode command)

Enter insert mode at the end of the current line

r (vi text editor mode command)

Replace one character with the next character entered

R (vi text editor mode command)

Enter replace mode and continue to replace (overwrite) characters (until escape

u (vi text editor mode command)

 undo the previous command

. (vi text editor mode command)

Repeat the last edit

n. (vi text editor mode command)

Repeat the last edit command n times

nk (vi text editor mode command)

Repeat command k n times

x (vi text editor mode command)

delete the next character

dw (vi text editor mode command)

delete the next word

dd (vi text editor mode command)

delete this line

D (vi text editor mode command)

delete from the cursor to the end of the line

yy (vi text editor mode command)

copy the current line into a buffer

p (vi text editor mode command)

paste any lines below current lines

:w <enter> (vi text editor mode command)

save the file

:w name <enter> (vi text editor mode command)

 save the file as name

:q <enter> (vi text editor mode command)

exit vi

:q! <enter> (vi text editor mode command)

exit vi without saving

:wq <enter> (vi text editor mode command)

save file and exit vi

Shell scripts are stored in text files that must be both ___ ___

readable and executable

All bash shell scripts should start with the following line, which alerts the bash interpreter to execute

 #!/bin/bash

Input is accomplished through the ____ statement, which is usually followed by a variable. It will result in the cursor blinking on a blank line.

read

Two common forms of conditional statements

variable comparison value and filetest filename

-eq

equal to

-ne

not equal to

-gt

greater than

-lt

less than

-ge

greater than or equal to

-le

less than or equal to

-d (filetest condition)

item is a directory

-e (filetest condition)

file exists

-f (filetest condition)

file exists and is a regular file

-h (filetest condition)

item is a symbolic link

-r (filetest condition)

file exists and is readable

-w (filetest condition)

file exists and is writable

-x (filetest condition)

file exists and is executable

What is the notation for executing a script

./script <enter>