Linux with Operating System Concepts



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n
recalls instruction 
n
from the list, and !
string
recalls the last instruction that 
matches 
string
.
• Home directory (~)—The user’s home directory, typically stored at /home/
username

can be denoted using the ~ (tilde) character. You can also reference another user’s 
home directory through ~
username
.
• Interpreter—A program that interprets code, that is, receives an instruction from 
the user, translates it into an executable form, and executes it. Linux shells contain 
an interpreter so that the user can enter commands in the shell via a command line.
• Java virtual machine—A program which contains a Java byte-code interpreter. Nearly 
all web browsers contain a JVM so that you can run compiled Java code allowing 
programmers to place compiled code on the Internet without having to worry about 
compiling the code for every available platform. This also protects the programmer’s 
intellectual property in that the code is not available in its source format so that peo-
ple cannot see how the program works.
• Long listing—The ls command in Linux lists the contents of the current (or specified) 
directory. The long listing displays additional information about the contents includ-
ing permissions, sizes, and owners.
• Man pages—Help information available for nearly every Linux instruction.
• Options—Linux instructions permit a series of options that allow the user to more 
concretely specify how the instruction should operate. For instance, ls permits –l to 
provide a long listing, -a to print hidden files, and so forth. To view the options, use 
the man page.
• Parameters—In addition to options, many Linux commands expect or permit param-
eters such as files to operate on.
• Pipe—A form of redirection in which the output of one Linux command is used as 
the input to another. The pipe operator is | which is placed between two commands 
such as 
ls –1 | wc -l
.
• Prompt—The shell presents a prompt when waiting for the user’s next command. The 
PS1 environment variable allows you to tailor the prompt. By default, it outputs the 
user’s name, the computer’s hostname, the current working directory, and either $ or 
# to indicate that you are a normal user or root.
• PS1 variable—This variable is predefined for users but the user can redefine it as 
desired. By default it is [\u@\h \W]\$ which means to output the user’s username, an 
@ symbol, the hostname, a space, the current working directory, all in [], followed 
by \$, the prompt character (usually either $ or #). This could be redefined to output 


66

Linux with Operating System Concepts
the current date, the current time, the command number (i.e., the number in the his-
tory list that this command will be stored as), and/or the result of the last command, 
among others.
• Redirection—The ability to change the direction of input or output of the command 
being specified. By default, most Linux commands accept input from a file, but this 
could be redirected to come from keyboard, and send output to the terminal window, 
but this could be redirected to go to a file. Redirection characters are 
<

<<
for redi-
recting input, 
>

>>
for redirecting output, and | for a pipe between two instructions.
• STDERR—Default output location for error messages.
• STDIN—Default input source for running programs.
• STDOUT—Default output for running programs.
• TC-Shell—A variation of C-Shell with updated features, many of which are found in 
Bash such as command line editing and filename completion.
• Wildcard—Characters that are used to represent other characters to match against 
in order to simplify file and directory specification. For instance, * means to match 
anything so that ls *.txt will list all files that end with .txt.
Linux commands covered in this chapter:
• alias—To define an alias, the form is 
alias 

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