Skip to content

Latest commit

 

History

History
54 lines (38 loc) · 1.39 KB

Slides04.md

File metadata and controls

54 lines (38 loc) · 1.39 KB
Raw

Step 4

Grokking grep

grep

Finds files based on their content

~ $ touch a b c
~ $ echo This sequence of characters is called a \"string\". > d
~ $ cat d
This sequence of characters is called a "string".
~ $ ls
a  b  c  d
~ $ grep is *
d:This sequence of characters is called a "string".

Famous quote

"Some people, when confronted with a problem, think 'I know, I'll use regular expressions.' Now they have two problems." - Jamie Zawinski

Regular expressions

A "regex" is a pattern for matching strings

  • dir *.txt - match zero or more characters
  • find //myserver/myshare/logs/000[4-9] -print
  • grep is * - find "is" in all files in current directory

Helpful regexes

  • one|other - find one pattern or the other.
  • ^ - pattern for the beginning of a line.
  • $ - pattern for the end of a line.
  • ? - match exactly one character.
  • * - match zero or more characters.
  • + - match one or more characters.
  • [A-Z] - match any character in a range (such as in this case any uppercase Latin alphabetic character).
  • [n|y] - match one character or another (such as n or y here).

Why 2 problems?

What does the following do?

(?bhttp://[-A-Za-z0-9+&@#/%?=~_()|!:,.;]*[-A-Za-z0-9+&@f
  • Checks a Web URL for validity
  • Are you going to remember that?
  • Are you going to be able to figure it out?