Shell Scripting FAQ’s

The two main advantages of shell scripting:

• It facilitates developing your own custom OS with relevant features which best suit your needs.
• It facilitates designing software applications according to their respective platforms.

csh,ksh,bash,Bourne . The most commonly used and advanced shell used today is "Bash" .

A shell script has two types of variables :

System-defined variables - they are created/defined by the Operating System(Linux) itself. These variables are generally defined in Capital Letters and can be viewed by “set” command.

User-defined variables - they are created or defined by system users and the values of variables can be viewed by using the command “echo”.

Shortcuts are created using "links" on Linux. There are two types of links that can be used namely "soft link" and "hard link".

Soft link is link to the file name and can reside on different filesytem as well. The hard link is the link to the inode of the file and have to be on the same filesytem as that of the file. Deleting the original file makes the soft link inactive (broken link) but does not affect the hard link (Hard link will still access a copy of the file)

There are mainly two kinds of shells in Linux OS, namely, Bourne Shell and C-Shell. Examples of derivative from each are as follows;

Bourne Shell: Bourne Shell, Bourne-Again Shell, Korn Shell, POSIX Shell.

C-Shell: C-Shell, TENEX C-Shell, Z-Shell

Arguments can be passed as:

scriptName "Arg1" "Arg2"…."Argn" and can be accessed inside the script as $1 , $2 .. $n

GUI scripting is used for controlling a computer and its applications. GUI scripting supports different applications. It mostly depends on the operating system.

$# shows the count of the arguments passed to the script.

We use single quotes where we don’t want to perform the variables’ evaluation to values.

We use double quotes where we want to perform the variables’ evaluation to values.

$@ treats each quoted arguments as separate arguments but $* will consider the entire set of positional parameters as a single string.

A Linux process passes through four stages:

Waiting: The Linux process waits for the resource.

Running: The Linux process is currently being executed.

Stopped: The Linux process is stopped after successful execution.

Zombie: The process has stopped but is still active in the process table.

Positional parameters are the variables defined by a Shell. They are used to pass information to the program by specifying arguments in the command line.

The test command is used to compare the text strings. The test command compares text strings by comparing each character in each string.

The Shebang line remains at the script’s top. It gives information about the location where the engine is, which executes the script.

A UNIX environment has only one Kernel and there are multiple Shells available.

The Shell programs are stored in a file called sh.

IFS refers to Internal Field Separator. It is a system variable whose default value is space, tab, following by a new line. IFS denotes where a field or word ends in a line and where another begins.

No, we don’t need a separate compiler to execute a Shell program. Since Shell itself is a command-line in the shell program and executes them.