College Online Material

Ghifari Nur

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Mar 16, 2021

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CLI or Basic Shell

The CLI

• Text-based interface
• Access via a terminal (GUI and Virtual)
• Commands passed to a shell
• Shell prompt (sysadmin@localhost/~)

Shell Features

• Command history — the ability to re-execute previous commands quickly
• Scripting — create programs by placing the command
• Alias — create a shortcut to longer commands
• Variables — store info that can be used to modify the functionality of the shell or commands

Understanding Command Structure

Command Format

• Basic format

command [options] [arguments]

Option change the behavior of commands

Arguments are used to provide addition info for a command

Command Options

• Vary based on command
• Older option formate: -a

-abc = -a -b -c$ls -al

• Newer (GNU) option format: — all

Command History

• View the previous command: history
• Bring up the previous command up arrow
• Modify previous commands: left right
• Execute a previous command: !<num>

Variables

Shell Variables

• Use to store the sys. info
• View with the echo command

$ echo $HISTSIZE

• Modify

$ HISTSIZE = 500

• Place command in ~/.bashrc to make permanent

Path Variable

• Determines where command are execute

$ echo $PATH
/c/Users/User Account/bin:/mingw64/bin:/usr/local/bin:/usr/bin:/bin:/mingw64/

Command Path

Find Command

• Hard to determine where a command is located
• Instead of searching directories in the PATH variable manually, use the which command

$ which cal
/usr/bin/cal$ which date
/usr/bin/date

Additional Command Structure

Globbing

• used to match sets of files in a dir.
• * match zero or more of any char.
• ? match exactly one of any char.
• [] match exactly one of a set of char.

$ touch a.txt && touch ab.txt && touch abc.txt
$ ls a*
a.txt  ab.txt  abc.txt$ ls *txt?

Quoting

• Double quotes “ — used to disable the meaning of some metachar. like globbing
• Single quotes ‘ — used to disable the meaning of all metachar.

can use \ to disable next char. only

$ echo "$SHELL"
$ echo '$SHELL'

Control Statement

• The ; char.— used to separate commands on a CLI
• The && char. — used to execute the second command if the first command succeds
• The || char. — used to execute the second command if the first command fails

$ sudo apt-get update && sudo apt-get upgrade -y
$ ls > count.txt; wc-l