Q: - What is
Shell's Responsibilities ?
ANS:The shell is
responsible for the execution of all programs that you request from your
terminal. Each time you type in a line to the shell, the shell analyzes the
line and then determines what to do.The line that is typed to the shell is
known more formally as the command line. The shell scans this command line and
determines the name of the program to be executed and what arguments to pass to
the program.
Q: - What is
"$#" Variable ?
The $# Variable
Whenever you execute a shell program, the special shell variable $# gets set to
the number of arguments that were typed on the command line.
Q: - Explain
"Exit Status" for a shell script ?
Whenever any
program completes execution under the Unix system, it returns an exit status
back to the system. This status is a number that usually indicates whether the
program successfully ran. By convention, an exit status of zero indicates that
a program succeeded, and nonzero indicates that it failed. Failures can be
caused by invalid arguments passed to the program, or by an error condition
detected by the program. For example, the cp command returns a nonzero exit
status if the copy fails for some reason (for example, if it can't create the
destination file), or if the arguments aren't correctly specified (for example,
wrong number of arguments, or more than two arguments and the last one isn't a
directory). In the case of grep, an exit status of zero (success) is returned
if it finds the specified pattern in at least one of the files; a nonzero value
is returned if it can't find the pattern or if an error occurs (the arguments
aren't correctly specified, or it can't open one of the files).
Q: - What is
"Command Substitution" ?
Command substitution is the process by which the shell runs a command and
replaces the command substitution with the output of the executed command. That
sounds like a mouthful, but it's pretty straightforward in practice.
Q: - What is
" eval" command ?
The eval command exists to supersede the normal command-line substitution and
evaluation order, making it possible for a shell script to build up commands
dynamically. This is a powerful facility, but it must be used carefully.
Because the shell does so many different kinds of substitutions, it pays to
understand the order in which the shell evaluates input lines.
Q: - What is awk
?
An awk invocation can define variables, supply the program, and name the input
files.
Q: - What is
"grep" programe ?
The grep program is the primary tool for extracting interesting lines of text
from input datafiles. POSIX mandates a single version with different options to
provide the behavior traditionally obtained from the three grep variants: grep,
egrep, and fgrep.
Q: - explain
"read" command ?
The read command is one of the most important ways to get information into a
shell program:
$ x=abc ; printf
"x is now '%s'. Enter new value: " $x ; read x
x is now 'abc'.
Enter new value: PDQ
$ echo $x
PDQ
Q: - What are the
two files used by the shell to initialize itself?
/etc/profile
profile
Q: - What is
Interactive mode?
Interactive mode
means that the shell expects to read input from you and execute the commands
that you specify. This mode is called interactive because the shell is interacting
with a user. This is usually the mode of the shell that most users are familiar
with: you log in, execute some commands, and log out. When you log out using
the exit command, the shell exits.
Q: - What is
noninteractive mode?
In this mode, the
shell does not interact with you; instead it reads commands stored in a file
and executes them. When it reaches the end of the file, the shell exits.
Q: - what is
local variable?
A local variable
is a variable that is present within the current instance of the shell. It is
not available to programs that are started by the shell. The variables that you
looked at previously have all been local variables.
Q: - What is
environment variable?
An environment
variable is a variable that is available to any child process of the shell.
Some programs need environment variables in order to function correctly.
Usually a shell script defines only those environment variables that are needed
by the programs that it runs.
Q: - What is
shell variable?
A shell variable
is a special variable that is set by the shell and is required by the shell in
order to function correctly. Some of these variables are environment variables
whereas others are local variables.
Q: - Explain the
“Exit” command?
Every program
whether on UNIX or Linux should end at a certain point of time and successful
completion of a program is denoted by the output 0. If the program gives an
output other than 0 it defines that there has been some problem with the
execution or termination of the problem. Whenever you are calling other
function, exit command gets displayed.
Q: - How do you
find out what’s your shell?
echo $SHELL
Q: - How you will
run a process in the background?
./ProcessName
&
Q: - How do you
write a while loop in shell?
Use While Loop
while [
condition ]
do
command1
command2
command3
done
Example
#!/bin/bash
x=1
while [ $x -le 5 ]
do
echo "Welcome $x times"
x=$(( $x + 1 ))
done
Q: - How do you
read keyboard input in shell scripts?
Use read command
Q: - What is GUI
Scripting?
Graphical user
interface provided the much needed thrust for controlling a computer and its
applications. This form of language simplified repetitive actions. Support for
different applications mostly depends upon the operating system. These interact
with menus, buttons, etc.
Q: - Explain the
term “loops”?
Loops enable you
to execute a series of commands multiple times. Two main types of loops are the
while and for loops.
Q: - What is
“Nested Loops”?
When a loop is
located inside the body of another loop it is said to be nested within another
loop.
Q: - What is
“Infinite Loops”?
Loops that
execute forever without terminating.
Q: - What is “File
Descriptor”?
An integer that
is associated with a file. Enables you to read and write from a file using the
integer instead of the file's name.
Q: - Explain
“STDIN”?
STDIN Standard
Input. User input is read from STDIN. The file descriptor for STDIN is 0.
Q: - Explain
“STDOUT”?
STDOUT Standard
Output. The output of scripts is usually to STDOUT. The file descriptor for
STDOUT is 1.
Q: - Explain
“STDERR”?
STDERR Standard
Error. A special type of output used for error messages. The file descriptor
for STDERR is 2.
Q: - Explain
“Escape Sequence”?
An escape
sequence is special sequence of characters that represents another
character.
Q: - Explain
“Output Redirection” in shell scripting?
In UNIX or Linux,
the process of capturing the output of a command and storing it in a file is
called output redirection because it redirects the output of a
command into a file instead of the screen.
Q: Explain “Input Redirection” in shell
scripting?
In UNIX or Linux
the process of sending input to a command from a file is called input
redirection.
Q: - What is “Field separator”?
The field
separator controls the manner in which an input line is broken into fields. In
the shell, the field separator is stored in the variable IFS. In awk, the field
separator is stored in the awk variable FS.
Q: - What is “Library”?
A file that
contains only functions is called a library. Usually libraries contain no main
code.
