Page 129 - DCAP106_OPERATING_SYSTEM_TOOLS

Operating System Tools

Notes Self Assessment

Fill in the blanks:
1. The ....................................... is a program that takes your commands from the keyboard and
gives them to the operating system to perform.
2. “#” specifies the administrator, called “.......................................”.
3. A ....................................... is a chain of characters representing a command which corresponds
to an executable file of the system.
4. A ....................................... in a shell script is a means of referencing a numeric or character
value.
5. The ....................................... is used to escape a single character that might otherwise be
treated as a special character by the shell.

7.2 Types of Shell

There are many different types of shells in the Linux operating system. These command-line
interfaces provide powerful environments for software development and system maintenance.
Though shells have many commands in common, each type has unique features. Over time,
individual programmers come to prefer one type of shell over another; some develop new,
enhanced shells based on previous ones.

Table 7.1 shows the different shells available in Linux:
Table 7.1: Different Types of Shell

Shell Name Developed by Where Remark
BASH (Bourne- Brian Fox and Chet Free Software Most common shell in
Again SHell) Ramey Foundation Linux. It's Freeware shell.
CSH (C SHell) Bill Joy University of The C shell's syntax and
California (for BSD) usage are very similar to the
C programming language.
KSH (Korn SHell) David Korn AT&T Bell Labs —
TCSH See the man page. — TCSH is an enhanced but
Type $ man tcsh completely compatible
version of the Berkeley
UNIX C shell (CSH).

In order to find all the available shells in your system, we type the following command:
$ cat /etc/shells
!

Caution Every shell does the same job, however each understands different command
syntax and offers different built-in functions.
These shells are discussed as below.

7.2.1 BASH (Bourne-Again SHell)

BASH, Bourne-again shell, is considered a free software UNIX shell which is written for the
GNU Project. BASH the name is a pun on the name of the Bourne shell (sh), an early and

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