My talk at the Linux Day 2016 in Rome.

1. #LinuxDay2016
http://lugroma3.org/

2. The Unbearable
Lightness
Extending the Bash shell

3. I have a natural revulsion to any operating system that
shows so little planning as to have named all of its
commands after digestive noises (awk, grep, fsck, nroff).
Source: The UNIX HATERS Handbook

4. Shellshocks

5. CVE-2014-6271
env x='() { :;}; echo vulnerable' bash -c "echo this is a test"

6. CVE-2014-7169
env X='() { (a)=>' bash -c "echo date"; cat echo

7. Weaknesses

8. http://mywiki.wooledge.org/BashWeaknesses

9. Speed
It's too big and too slow.
Source: man bash

10. Everything is text
egrep '^To:|^Cc:' /var/spool/mail/$USER |
cut -c5- |
awk '{ for (i = 1; i <= NF; i++) print $i }' |
sed 's/,//g' | grep -v $USER | sort | uniq

11. Floating point
$ echo $((3/2))
1

12. Multidimensional
arrays
$ array=('d1=(v1 v2 v3)' 'd2=(v1 v2 v3)')
$ for elt in "${array[@]}";do eval $elt;done
$ echo "d1 ${#d1[@]} ${d1[@]}"
$ echo "d2 ${#d2[@]} ${d2[@]}"

13. Sorting
$ array=(2 1 0)
$ IFS=$'n' sorted=($(sort <<<"${array[*]}"))
$ unset IFS
$ echo ${sorted[*]}
0 1 2

14. Variable typing
$ declare -i x
$ x=foo
$ echo $x
0

15. Variable scope
Local vs Global vs Environment

16. Return values
Bash functions don't return anything (except numbers in the
range 0-255); they only produce output streams

17. Passing by
reference
function swap()
{
eval "$1=${!2} $2=${!1}"
}
$ x=a y=b
$ swap x y
b a

18. Function scope
$ shopt -s extdebug
$ function foo() { echo $qux ; echo ${BASH_ARGV[0]} ; }
$ function bar() { local qux=thud ; foo ; }
$bar baz
thud
baz

19. Function collapsing
chatter() {
if [[ $verbose ]]; then
chatter() {
echo "$@"
}
chatter "$@"
else
chatter() {
:
}
fi
}

20. No closures
No first-order functions, no lambdas, ...

21. Try/catch
trap

22. Exception handling
set -e

23. Process
management
select? poll? events?

24. Parsing
sed
-ne "s|^($s):|1|"
-e "s|^($s)($w)$s:$s["'](.*)["']$s$|1$fs2$fs3|p"
-e "s|^($s)($w)$s:$s(.*)$s$|1$fs2$fs3|p"

25. Binary data
dd if=/dev/brain of=/dev/null

26. Paradigms
OO? Functional? Flow-driven? Reflective?

27. Security
Did you say dropping permissions?

28. Large programs
source foobar.sh

29. Debugging
set -x

30. Subshell Dilemma
$ c=0; ls * | while read i; do ((c++)); done; echo $c
0

31. Bashisms
eval x=$$x

32. Portability
It is easier to port a shell than a shell script.
Source: Larry Wall

33. Why does it
matter?

34. DRY
Don't write scripts, write libraries

35. DevOps
Python/Ruby/Scala/... are not ubiquitous

36. Legacy code

37. Attempts

38. bang.sh
the "b" namespace

39. bashinator
function createDirectory() {
local directory=${1}
if [[ -z "${directory}" ]]; then
__msg err "argument 1 (directory) missing"
return 2
fi
__msg debug "directory: ${directory}"
if ! mkdir -p "${directory}" >> "$_{L}" 2>&1; then
__msg err "failed to create directory '${directory}'"
return 2
fi
return 0
}

40. bash automated
testing system
@test "addition using bc" {
result="$(echo 2+2 | bc)"
[ "$result" -eq 4 ]
}
@test "addition using dc" {
result="$(echo 2 2+p | dc)"
[ "$result" -eq 4 ]
}

41. bash infinity
import util/namedParameters util/class
class:Human() {
public string name
public integer height
public array eaten
Human.__getter__() {
echo "I'm a human called $(this name), $(this height) cm tall."
}
...
}

42. bash manager
hello:
p1=World!
$ ./bash_manager.sh -h /tmp/helloHome
Hello World!

43. bash toolbox
alias fail='printf "${BASH_SOURCE##*/}: ${FU ...
alias debug='printf "${BASH_SOURCE##*/}: ${FU ...
alias caller='nm=$(builtin caller 0); nm=${nm% ...

44. bashworks
Inversion of control: the overall program's flow of control
is not dictated by the caller, but by the framework.
Polite functions: Generic reuseable functions usually take a
module name string argument.

45. blp
minimalist approach

46. log4sh
# set alternative 'nc' command
log4sh_setAlternative nc /bin/nc
# add and configure a SyslogAppender that logs to a remote host
logger_addAppender mySyslog
appender_setType mySyslog SyslogAppender
appender_syslog_setFacility mySyslog local4
appender_syslog_setHost mySyslog somehost
appender_activateOptions mySyslog
# say Hello to the world
logger_info 'Hello, world'

47. mbfl
mbfl_argv_all_files ||
exit_because_wrong_command_line_arguments
for item in "${ARGV[@]}"
do
test "${script_option_AUTO}" = yes && {
size=$(mbfl_file_get_size "${item}")
...

48. oobash
## class Dialog
Dialog=(
# Explicit definition is needed to make inheritance possible.
function __new__ = Dialog::__new__
function __delete__ = Dialog::__delete__
)

49. ticktick
. ticktick.sh
function printEmployees() {
for employee in ``people.Engineering.items()``; do
printf " - %sn" ${!employee}
done
}

50. Bashlets

51. Modular
source bashlet datatype/version
bash$$ version sort 1.44 1.4 1.4.4 1.4.4a 1.4-1234

52. Git integration

53. General-purpose
IPC, math, network, OS-abstraction, parsers, UX, ...

54. Extensible
Plugins for web protocols, databases, RCS, ...

55. Smart autoloading
Via introspection

56. Work in progress

57. Colophon
vim, Hovercraft!, CentOS Linux 7.2

58. exit 0
Roberto Reale
https://bashlets.sh
https://github.com/bashlets