lesson 4 and 5 command line and aliases

8/7/2019 Lesson 4 and 5 Command Line and Aliases

1/19

The Command Line

The Exit Status($?)

Multiple Commands and command

grouping(;) Conditional execution of

commands(&& and ||)

Commands in the Background(&) Command-Line History(history)


2/19


3/19

Exercise

Execute the following commands

Example 1

$grep oracle /etc/passwd

$echo $?

Example 2

$grep ellie /etc/passwd

$echo $? What do you notice about the exit status of both

commands?


4/19

Grouping commands

The ; is used to group multiple commandsin a command line

Each command is separated by a semi-colon and the command line is terminatedby a new line


5/19

Exercise

Type the following commands at theprompt

$cal;pwd;date

Question: What do you notice regarding

the output of the 3 commands?


6/19

Conditional execution ofcommands(&& and ||)

If you have two commands separated by&& characters, the second command will

only execute if the first succeeds.

If you have two commands separated by ||characters, the second command will onlyexecute if the first fails.


7/19

Exercise

Run the following commands at the command prompt

Example 1

$cal && pwd

Example 2 $cal -o && pwd

Example 3

$cal -o || pwd

Did you notice that the second command in example 2did not run because the first failed?

What did you notice about example 3?


8/19

Commands in the Background(&)

The & is used to execute a command inthe background

It gives you the convenience of executingother commands at the prompt

Since the output of a backgroundcommand usually goes to the screen, it isa good practice to redirect the output to afile using the output redirection command


9/19

Exercise


Example 1

$sleep 50 Example 2

$sleep 100 &

What differences did you notice in the twocommands?


10/19

Command-Line History(history)

The history command is used to view thehistory of all the commands you havetyped since your session started.

The default name of the history file is.sh_history and it is locate in your homedirectory ( or ~/)

The $HISTSIZE variable specified in/etc/profile is used to specify the maximumnumber of entries in the file


11/19

Command-Line History(history)

Contd. The r command is used to re-execute a

command in the history file.

$ r n (Where n is the serial number ofthe command in the history)


12/19

Exercise

Execute the following Example 1 $echo $HISTSIZE Example 2

$echo $HISTFILE Example 3 $history Example 4

$ r n Where n is a number in the output of example 3above. Did you notice that the command was re-executed?


13/19

ALIASES

Listing Aliases

Creating Aliases

Deleting Aliases


14/19

Listing Aliases

An Alias is a user-defined or korn shellabbreviation of a command

The alias built-in command lists setaliases

Default aliases are provided by theshell and can be redefined.

For example the history command is analias for the fc -l command


15/19

Exercise

List all defined aliases by executing thecommand below

$alias


16/19

Creating Aliases

A user can create alias in the korn shell

If an alias is defined in the .profile file, itpersists all sessions but if you definean alias at the prompt, the alias is unsetwhen you log off.

$alias cl=clear

If you defined an alias as in the above,you only have type cl to clear yourscreen.


17/19

Exercise


Example 1

$alias list=ls -l Example 2

$list


18/19

DELETING ALIASES

The unalias command is used to unsetaliases


19/19

Exercise


Example 1

$list Example 2

$unalias list

Example 3 $list

lesson 4 and 5 command line and aliases

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