Intro to Linux Shell Scripting

Intro to Shell Scripting

Vern CederCanterbury School

Shell Scripting

An Introduction to Linux Shell Scripting

Vern CederCanterbury School, Fort Wayne



This talk ISN'T for

# Experienced shell scripters

# People who own Tshirts saying “Go away or I will replace you with a very small shell script”

# Anyone with a favorite shell hack they MUST share... ;)



This talk is for you if...

# You can open a terminal

# You can type

# You're interested in how to combine those two things to make your life easier



What's Coming

# Why use the shell?

# Basic shell commands

# Combining shell commands

# Creating simple scripts

# Automation with cron



Do you...



$ Need to manage computers not on your desk?

$ Need to perform complex operations, on lots of files?

$ Need to repeat the same operations on a lot of machines?

$ Wish that some of this routine stuff could just happen?



What's a “shell”?

# A program that uses (text) commands to talk to the OS

# DOS (e.g.)

# sh, bash, csh, ksh, zsh, etc...

# This talk will assume bash



Basic Shell Commands

# Files – ls, cp, mv, rm, mkdir

# Access – chmod, chown

# Disks – df, mount

# Processes – ps, kill, fg, bg

# Network – ifconfig, ping, tracepath



Take ls, for example

# ls

# ls l

# ls a

# ls t

# ls R

# ls latR

list files

list more info

list ALL

list by date

list Recursive

or combine



More file commands

# cp a b

# mv a b

# rm a

# rm rf a

copy files

move (rename)

delete

remove EVERYTHING (danger, danger)



Access commands

# chown user:group a

# chmod ugo+rwx a

change file owner

change permissions



disk commands

# df

# du /folder

# mount

get free space

get amount used

show/change disks mounted



process commands

# ps ax

# kill processid

# fg

# bg

show processes

kill a process

foreground

background



network commands

# ifconfig

# ping

# tracepath

show interfaces

ping a host

follow a packet



So you can...

# Manage files

# Monitor disks

# Control user access

# Manage/debug network connections



DANGER!

You can also...

Completely destroy your system

Don't experiment/practice as root!



But how do you know what does what?

# Man – the best way to find out what a command does

# Apropos – the way to find the right command

# tldp.org – man pages and howto's

# Google ;)



So?

How is this better than using a file manager?

# Powerful – you can do ANYTHING

# Remote – you can do it from ANYWHERE

# “Combinable” (that's next)



The “unix idea”

# Small, specific utilities

# Text input/output

# “pipes” to connect one utility to another



Commands to pull it all together

# cat

# grep

# cut

# sort

# uniq

# head, tail

# more, less

dump file

find a pattern

cut out a field

sort

remove dupes

get part of file

page through file



Introducing the “pipe”

# | connects the output of one command to the input of another

# > (and >>) puts the output into a file

# < puts a file to input



For example...

Find out who is hogging the home disk...

# du

# sort

# tail

# du cks * | sort rn | head



Another example...Who's tried to log into your box?

# cat

# grep

# cut

# sort

# uniq



Scripts

# To avoid retyping (and sometimes refiguring out)

# To handle more complex chores



Creating a simple script

# Text file (text editor)

# The “shebang” line

# Shell commands

# Make it executable



“space hog” as script

#!/bin/bash

du cks $1 | sort rn | head



What I didn't cover(a very partial list)

# find

# tar

# environment vars

# echo

# sleep

# editors

# Sed & awk

# cron & crontab

# loops

# if

# test ( [ ] )



But what about automation?

What if you need to repeat the same script every month? Every week? Every day? Every hour? Every minute?



Automating with cron

# cron lets you run scripts at any time, as any user



Print Resources

# Classic Shell Scripting, Robbins & Beebe, O'Reilly

# Think Linux, Jon Lasser, QUE

# UNIX Hints and Hacks, Kirk Waingrow, QUE

# Linux in a Nutshell, Ellen Siever, et al. O'Reilly

# Many books on Linux/UNIX automation and administration



Web Resources

# See http://tech.canterburyschool.org/tech/shell

# Google “linux shell scripting” or the like

http://tech.canterburyschool.org/tech/shell



Video Resources

# http://video.google.com

Search for “linux shell scripting tutorial”

http://video.google.com/

Intro to Linux Shell Scripting

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