A Brief and incomplete overview of Shell Script, Bash and some commands.

1. https://commons.wikimedia.org/wiki/File:Bivalve_Sea_Shell.png
SHELL SCRIPT

2. SHELL SCRIPT
IN A
NUTSHELL
https://commons.wikimedia.org/wiki/File:Noix_Fernor_Cl_J_weber06_(23675300905).jpg

3. SHELL SCRIPT
IN A
NUTSHELL
http://www.dublinconcerts.ie/band/xzibit/

4. Why
“in a nutshell?”

5. Scripting is
more practice
than concepts.

6. How can shell
script help me?

7. “Many C/C++/Java candidates, even some with
10+ years of experience, would happily spend a
week writing a 2,500-line program to do
something you could do in 30 seconds with a
simple Unix command.”
– Steve Yegge
https://sites.google.com/site/steveyegge2/five-essential-phone-screen-questions

8. How can shell scripts help me?
● As developers, we make computers work for
others.
● Computers could work a lot for ourselves, too.
● Shell script is a faster way to get work done.

9. Which shell
should I use?

10. Whatever you prefer!
(But we will talk about Bash here.)

11. How good is
shell script?

12. How good is shell script?
● Very good for quick, one-off tasks.
● Great for small tasks.
● Also good to deal with a lot of files, download
stuff.
● Great option to automate a set of steps.
● Can get confusing fast.
Peter H. Salus. A Quarter-Century of Unix apud http://www.catb.org/~esr/writings/taoup/html/ch01s06.html

13. “Python [and other languages -me] scales up to
thousand of lines, shell script scales down to a
few keystrokes.”
– Somebody at Stack Overflow
Alas, I couldn’t find the link, not even the name of the user :(

14. Unix Philosophy

15. Unix Philosophy
● Write programs that do one thing and do it well.
● Write programs to work together.
● Write programs to handle text streams.
Peter H. Salus. A Quarter-Century of Unix apud http://www.catb.org/~esr/writings/taoup/html/ch01s06.html

16. Unix Philosophy
● Small utilities.
● Pipes and redirects.
● “Everything is a file.”
– Including standard input/output/error.
Peter H. Salus. A Quarter-Century of Unix apud http://www.catb.org/~esr/writings/taoup/html/ch01s06.html

17. Simplest
Tools

18. echo
● Print content to standard output.

19. echo
$ echo This is my message.
This is my message.

20. echo
$ echo "This is my message."
This is my message.
$ echo 'This is my message.'
This is my message.

21. echo
$ echo -e 'JavanC++'
Java
C++

22. cat
● Concatenate files.
● Good for showing content.

23. cat
$ echo -e "JavanC++" > languages
$ cat languages
Java
C++

24. cat
$ echo -e "WindowsnLinuxnMac OS" > OSes
$ cat languages OSes
Java
C++
Windows
Linux
Mac OS

25. Quoting
and
Escaping

26. https://twitter.com/YossiKreinin/status/778552625310625792

27. Quoting and Escaping
$ echo This is my message.
This is my message.
$ echo "This is my message."
This is my message.
$ echo 'This is my message.'
This is my message.

28. $ echo Good times (are coming)
bash: syntax error next to unexpected `token' `('
$ echo "Good times (are coming)"
Good times (are coming)
$ echo 'Good times (are coming)'
Good times (are coming)
Quoting

29. $ echo Good times (are coming)
bash: syntax error next to unexpected `token' `('
$ echo "Good times (are coming)"
Good times (are coming)
$ echo 'Good times (are coming)'
Good times (are coming)
Quoting

30. $ echo This is a little star: *
This is a little star: languages OSes
$ echo 'This is a little star: *'
This is a little star: *
$ echo This is a little star: *
This is a little star: *
Escaping

31. What if my parameter
has quotes?

32. $ echo "This is Dave's "situation.""
This is Dave's "situation."

33. What if my parameter
both types of quotes?

34. $ echo "This is Dave's situation."
This is Dave's situation.

35. $ echo This is a "situation."
This is a situation.
$ echo 'This is a "situation."'
This is a "situation."
$ echo "This is "Dave's situation.""
This is "Dave's situation".
Quoting

36. https://twitter.com/YossiKreinin/status/778552625310625792

37. Variables

38. $ VAR=this
$ echo My value is $VAR
My value is this
$ echo "My value is $VAR"
My value is this
$ echo 'My value is $VAR'
My value is $VAR
Variables

39. $ EXAMPLES=quotes
$ echo "too ""many """$EXAMPLES""""""""
too many quotes
$ echo '"too ""many """$EXAMPLES""""""""'
"too ""many """$EXAMPLES""""""""
$ echo '"too ""many """'$EXAMPLES'""""""""'
"too ""many """quotes""
Variables

40. https://twitter.com/YossiKreinin/status/778552625310625792

41. The Triad of
Searching

42. grep
● Search for lines in one or more files.
– Or from standard input.
● “Basic” or “extended” regular expressions.
– Or even plain strings and PERL regexes.
● Many options
– Inverse match.
– Only match.
– Show line numbers...

43. grep
$ cat phones.txt
Pedro (81) 9 9653 7734
Paulo (81) 9 8614 1092
Paula (61) 9 8112 6751
Judite (61) 9 9612 9222

44. grep
$ grep '(61)' phones.txt
Paula (61) 9 8112 6751
Judite (61) 9 9612 9222
$ grep 'P.*o ' phones.txt
Pedro (81) 9 9653 7734
Paulo (81) 9 8614 1092

45. grep
$ cat phones2.txt
John (732) 554 8749
Phillip (552) 982 9839
Paul (882) 830 3802
Jared (893) 923 3820
$ echo *
languages name OSes phones2.txt phones.txt

46. grep
$ grep Paul *
phones2.txt:Paul (882) 830 3802
phones.txt:Paulo (81) 9 8614 1092
phones.txt:Paula (61) 9 8112 6751

47. sed
● A little weird programming language.
● Most of the time, we use the s/// command.
● Can alter the file inline.

48. sed
$ sed 's/Judite/Judith/' phones.txt
Pedro (81) 9 9653 7734
Paulo (81) 9 8614 1092
Paula (61) 9 8112 6751
Judith (61) 9 9612 9222

49. sed
$ cat phones.txt
Pedro (81) 9 9653 7734
Paulo (81) 9 8614 1092
Paula (61) 9 8112 6751
Judite (61) 9 9612 9222
$ sed -i 's/Judite/Judith/' phones.txt
$ cat phones.txt
Pedro (81) 9 9653 7734
Paulo (81) 9 8614 1092
Paula (61) 9 8112 6751
Judith (61) 9 9612 9222

50. awk
● A full-fledged programming language.
– Similar to (predecessor of) Perl, PHP.
– Most programmers would be comfortable with.
● Read files as tables.
– Each line is a record.
– Each space-separated part a column.

51. awk
$ awk '$1 == "Paul"{print}' *
Paul (882) 830 3802
$ awk '$1 ~ "Paul"{print}' *
Paul (882) 830 3802
Paulo (81) 9 8614 1092
Paula (61) 9 8112 6751

52. Pipes
and
Command
Substitution

53. Pipes
● Redirect standard output from one command to
another command’s standard input.
● Can also redirect standard error, sure.
● This is how most of the magic happens :)

54. Pipes
$ cat phones.txt
Pedro (81) 9 9653 7734
Paulo (81) 9 8614 1092
Paula (61) 9 8112 6751
Judith (61) 9 9612 9222

55. Pipes
$ cat phones.txt | grep '^P'
Pedro (81) 9 9653 7734
Paulo (81) 9 8614 1092
Paula (61) 9 8112 6751

56. Pipes
$ cat phones.txt | grep '^P' | sed 's/ [0-9]+$/ ****/'
Pedro (81) 9 9653 ****
Paulo (81) 9 8614 ****
Paula (61) 9 8112 ****

57. Command Substitution
● Adds one command’s output to another
command.

58. Abrupt End