Page 133 - DCAP106_OPERATING_SYSTEM_TOOLS

Operating System Tools

Notes Table 7.2: Differences between internal and external commands

Table 7.2: Differences between Internal and External Commands
External Linux Commands Internal Linux Commands
External commands are executed Internal commands are executed by the shell.
by the kernel.
A separate process is spawned No new process is created.
every time a new external
command is executed.
These are separate files in /bin These are built-ins in the shell. The execution of these
directory. The execution of these commands happens through the execution of their
commands happens through the corresponding files in /bin directory.
execution of their corresponding
files in /bin directory.
A few examples are cp, mv, etc. Some examples are cd, pwd, etc.

Task Illustrate the execution of external commands.

Self Assessment

Fill in the blanks:
11. ....................................... commands are those which are directly executed by the shell.
12. ....................................... commands are files present in the $PATH.

13. If the output states that the command is shell ......................................., it is an internal
command.
14. The execution of internal commands happens through the execution of their corresponding
files in ....................................... directory.
15. External linux commands are executed by the .......................................

7.4 Summary

z z The shell is a program that takes your commands from the keyboard and gives them to the
operating system to perform.
z z The shell provides an interface to Linux where you can type or enter commands using the
keyboard. It is known as the command line interface (CLI).

z z A variable in a shell script is a means of referencing a numeric or character value.
z z BASH is a free software UNIX shell written for the GNU Project. Its name is an acronym
which stands for Bourne-again shell.

z z The C shell (csh) is a Unix shell which added many feature improvements over the Bourne
shell, such as aliases and command history.

z z The Korn shell (ksh) is a Unix shell which is backwards-compatible with the Bourne shell
and includes many features of the C shell as well.

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