Shell Script
3 likes214 views
This document provides an introduction to shell scripting. It discusses how shell scripts can help automate tasks and make computers work for developers. Some key points covered include: - Shell scripts are useful for quick, one-off tasks and automating repetitive steps. They allow getting work done faster. - Common shell scripting tools like echo, cat, grep, sed, and awk are introduced along with examples of their usage. - Concepts like piping output between commands, command substitution, quoting, escaping and variables are explained. - The Unix philosophy of small, modular programs that work together is discussed in the context of shell script design.
![“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 :(](https://image.slidesharecdn.com/shell-script-170623021620/85/Shell-Script-13-320.jpg)
![Pipes
$ cat phones.txt | grep '^P' | sed 's/ [0-9]+$/ ****/'
Pedro (81) 9 9653 ****
Paulo (81) 9 8614 ****
Paula (61) 9 8112 ****](https://image.slidesharecdn.com/shell-script-170623021620/85/Shell-Script-56-320.jpg)
Shell Script
- 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
- 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
- 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
- 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
- 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