Bash is a widely used command line shell for Linux and other Unix-like operating systems. The presentation discusses the history and evolution of Unix-based systems and introduces some of the key features of the Bash shell, including built-in commands, external commands, variables, expansion, loops, conditionals, I/O redirection, and user input handling. It highlights new features introduced in Bash version 4 such as associative arrays, expanded string manipulations, and coprocesses.

1. Bash 4
Linux Open Administration Days
Pieter Colpaert_

2. #Understanding Bash
>A little history
>Reinventing UNIX
#Speaking Bash
#Bash 4
#_

3. Understanding Bash_

4. A little history (1970)

5. And some UNIX today (2010)
CC BY-SA – Larry Miller

6. But also
#Routers
#Mainframes
#Servers
#Smartphones
#PDA's
#Toasters
#..._

7. Let's reinvent UNIX
/rules/1# Writing software is one thing.
Making it communicate is another_

8. Let's reinvent UNIX
#Communication
>Systemcalls to
hardware through
kernel
>Systemcalls to user
through a
scriptinglanguage_

9. Why Bash?
#Not much knowledge required
#Combines C-shell, Bourne Shell, …
#Free Software
#_

10. What the hell is wrong with a GUI?
#Nothing
>For once in a life-time configurations
>Living today is pretty awesome
#Everything
>When you have to configure 20 PC's the same way
>When you don't want to install a demo-version of
some proprietary tool
>When you want to do things fast_

11. Speaking Bash_

12. Built-in commands
&, (( )), ., :, [, [[, alias, bg, bind, break, builtin,
caller, case, cd, command, compgen, complete,
compopt, continue, coproc, declare, dirs, disown,
echo, enable, eval, exec, exit, export, false, fc, fg,
for, for, function, getopts, hash, history, if, jobs, kill,
let, local, logout, mapfile, bind, printf, pushd, pwd,
read, readarray, readonly, return, set, select, shift,
shopt, source, suspend, test, time, times, true,
typeset, ulimit, umask, unalias, unset, until,
variables, wait, while, { cmd; }

13. External commands
#Compiled programs
#Bash-scripts
#Alias-commands
#Perl-scripts
#Functions
#_

14. man-pages
#If you don't know how a command works
>man command
>info command

15. Hello World!
On stdout:
#echo hello world!
On stderr:
#echo hello world! >&2
To a file:
#echo hello world! > HELLOWORLD
To the end of a file:
#echo hello world! >> HELLOWORLD

16. Input
###################In script
#read a b c
#set -
Set your $IFS!
###################From CLI
#Script.sh < file
#Here document:
#script.sh <<EOF

17. Scripting Basics
#Magic - #!/bin/bash
#Add -x to debug
#Comments - #
#; = EOL
# escapes EOL
#chmod +x
#echo $PATH

18. Expansion
#VARIABLE=value
>All-caps not needed, just recommended
#echo ${VARIABLE}
>{} not always needed, but stops problems
>$ is necessary
#declare -i VARIABLE=value
>Specifies variable is an integer

19. Expansion
#Command Substitution
>$(command)
>`command`
#Tilde
>~ = your home directory
>~user = user's home directory
#Wildcard globs
>man 7 glob

20. Expansion
#Prevention
> escapes a single special character
>“” escapes all but $, ` and
>'' escapes all special characters

21. Loops
#for VAR in items in list; do commands; done
#exit status - $?
#test - [ condition ]
#while [ test ]; do commands; done
#until [ test ]; do commands; done

22. Conditional Statements
#Operators
>&&
>||
#if [ test ]; then commands
#elif [ test ]; then commands
#else commands
#fi

23. Conditional Statements
#case VAR in
>option)
>commands
>;;
>*)
>commands
>;;
>esac

24. I/O Redirection
#Combining 1 and 2
>&>
>&>>
>2>&1
>>&2
#Channel 0 – STDIN
><
>-

25. User Input
#Arguments
>$1, $2, ${10}, etc.
>$* or $@
>$#

26. Bash 4_

27. Bash4
#Associative arrays!
#Expansions ~ perl
#Coproc
#..._

28. Associative Arrays
#Declare -A array
#array[element]=hello
#echo ${array[element]}

29. New expansions
Substring
#${#:0:1}
Case modification
#${var^^}
#${var^}
#${var,}
#${var,,}

30. Chopping strings
Get the extension of the current script
#${0##*.}
#${0#*.} (not correct)
Get the filename without extension
#${0%.*}
#${0%%.*} (not correct)

31. Examples

32. Questions
#CC BY-SA