1. Quiz 30 minutes 10 questions No talking, texting, collaboration, etc…

2. Review Please turn in your homework and practicals Regular Expressions

3. To generate #1 albums, ‘jay --help‘ recommends the -z flag

4. You’ve Already Used Them grep -i ‘documentroot’ httpd.conf Our command is grep The flag/option is –i for case insensitive httpd.conf is our file (Apache config file) ‘documentroot’ is our regex Called a ‘static string’ – means it doesn’t’ change

5. Regular Expression A regular expression (or regex) is “a sequence of characters that forms a search pattern” Awesome, thanks again Wikipedia, you’re always so descriptive It’s a set of characters with special meaning to capture another set of characters and either print them out, or modify them (substitute, etc…) Today we’re only looking at printing them out – matching

6. Static Strings Most simple regex grep -i ‘documentroot’ httpd.conf grep ‘error’ /var/log/messages What you’re matching on is one exact thing Also, I’m only using grep, we’ll get into other utilities later

7. Non-Static Strings More complex Uses ‘metacharacters’ to perform ‘abstraction’ Metacharacters – a ‘known’ set of characters like * or [ or + or. Abstraction – a way of referencing a more general group than what is explicitly stated grep [st]+ httpd.conf [ ] and + are metacharacters

8. Metacharacters [ ] indicates a single character range [a-z] would be any lowercase letter – grep [a-z] teams.txt [aeiou] would be any vowel [0-9] is any number Single-character range – grep ‘[Ss]eattle’ teams.txt – [hl][io] would match hi, ho, li, lo Not hl or io

9. Metacharacter Placement ^ is the beginning of the line – grep ‘^Seattle’ teams.txt – Case-sensitive (S not s) $ is the end of the line – grep ‘Bears$’ teams.txt

10. Your Turn grep ‘[Ss]ea’ teams.txt grep ‘^Rodgers’ anyfile.txt grep ‘horrible$’ anyfile.txt grep ‘[JFMASOND][aepuco][nbrynlgptvc]’ dates.txt

11. What The…? ‘[JFMASOND][aepuco][nbrynlgptvc]’ Regex’s get wonky quickly Keep It Simple This is too complex, but we still have to read it So break it down left to right [] matches what?

12. A Little More Sense ‘[JFMASOND][aepuco][nbrynlgptvc]’ So it will match J or F or M or A or S, etc… Followed by a or e or p or… Ja or Je, Fa or Fe Oh, and n or b or r or y Jan or Jen or Fan or Feb Names? Or something else?

13. Confusion Regins!. is any single character (not letter) – grep ‘^.b’ would match anything that had be as the second character in the line + and * are “multiples” – In the shell * is a wildcard, NOT in regex’s! – + means “at least one of” whatever came before it – * means “0 or more of” whatever came before it – grep ‘t+’ httpd.conf – grep ‘Bears*’ teams.txt.* is a common way of saying “keep going” – grep ‘^Rodgers.*horrible$’ anyfile.txt

14. One last bit of confusion Inside the [] the ^ means “not” So [^ab] means any character that’s not a or b ^[ab] means when a or b is at the beginning of the line grep ‘^[^A-Z]’ teams.txt – Any line that does not start with a capital letter

15. Escape the Regex (But Not) What if we wanted to search for a [ or. character? We would have to ‘escape’ it with \ grep ‘\[‘ pslist – root 1175 2 0 00:38 ? 00:00:01 [flush-253:0] So how would I search for a dollar amount?

16. Case Study We have a text file full of email addresses First, most obvious What if we added the.com domain? We can have.’s in the first part, but let’s say none in the second.

17. Follow-Up With every regex think – Can I do this easier another way? Just because you can use regex’s doesn’t mean you should – Is my regex as simple as possible? Know the limitations, no regex is perfect, but a lot of them are over-complicated – How is my data formatted? If it’s “regular” data in exactly columns with values in each spot use awk (next Weds)

18. Own Study Regular Expressions