CISC 5500 Data Analytics Tools and Scripting Special characters; - - PowerPoint PPT Presentation

CISC 5500 Data Analytics Tools and Scripting

Special characters; permissins; processes; vi

Computer and Information Science

Fordham University

Table of contents

• 1. vi
• 2. Special characters in Bash (expansions and substitutions)
• 3. File Permissions
• 4. Processes

1

review

• essential commands: pwd, cd, ls, cp, mv, rm, mkdir
• important commands: man, cat, more/less,
• very useful commands: wc, head, tail
• I/O redirection: >, >>, <, |
• what is a script

2

vi

vi

Difgerent modes:

• command mode (example commands: i x r R o O dd p A $ :)
• insert mode (ESC back to command mode)
• ‘command-line’ mode

3

Special characters

Special characters

Every command and its options, arguments are made of characters. Which characters are ‘regular’, not ‘special’? Alphabets, digits, underscores. The obviously special ones: spaces, ‘pound sign’ #, quotes. A useful command: echo

4

asterisk and tilde

• * - pathname expansion (the wildcard to match any characters

in a pathname)

• ∼ - home directory expansion

5

arithmetic expansion $$(( ))

Include simple computation in the command or the script

• only integers
• supported operations: +, -, *, /, %, **
• space is NOT signifjcant
• can be nested or include parenthesis

echo $((5+ $((7-6)) )) echo $((5+ (7-6) ))

6

brace expansion (list)

Two types:

• 1. comma-separated list
• 2. range of integers or single character
• it can have a preamble and/or a postscript
• it can be reversed
• no space embedded

echo front-{a,b,c}-back echo backward: {100..95} echo front-{a, b, c}-back # wrong!

7

variables (parameter expansion)

‘variables’: store the value for later use x=7 echo $x Pay attention to the spaces

8

Command substitute

execute a command and replace with its result using backtick ̀ or $( ) echo my name is `whoami` echo yes, it is $(whoami) echo and the current time is `date`

9

double quotes vs single quotes

double quotes suppress special character (thus expansion) except for $, \, and ̀ Particularly, spaces single quotes leave the quoted more ‘literal’ (less expansion) echo * echo "*" echo "$USER" echo '$USER'

10

escape characters

Backslash \ makes special characters ‘normal’ characters. How does it work together with quotes? echo $USER echo \$USER echo "$USER" echo "\$USER"

11

Permissions

users and groups in Linux

Users – every user has an ID and a name Groups - each user can belong to multiple groups What is the primary group? Command to fjnd out identity information id

12

Linux fjle permissions

What do we see from ls -l command? three ‘targets’: owner, group, all three permissions: read, write, execute

Table 1: Type/permission fjelds

type

• wner

group everyone ? rwx rwx rwx

13

change fjle permissions

Two ways of using chmod command (change the permission)

• 1. set
• 2. modify – u for owner

chmod 740 fjle2 chmod u+x fjle1 binary/octal representation r:4, w:2, x:1 4+2+1 = 7

14

Processes

processes

What is a process? ps command Options: -ef top command kill command

15

run a process in the background

some-command & nohup some-command & Other related commands exit nice

16

Summary

• special characters
• permissions
• processes
• vi

2020.9.3 17

Questions?

17

keyboard tricks and command history

up arrow brings back the previously used command tab key auto-completes path names history command

programmer’s jokes

• There are 10 types of people in this world...
• Why do programmers get confused between Halloween and

Christmas?

”With great power comes great responsibility”

Command su Substitute user – you need superuser password Command sudo As another user – confjgured by the superuser