Regular expression magic

REG EX: Regular Expressions Patterns

also called REGEXP

• String matching - not limited by specific characters, are flexible

• Standard syntax
  • Preg - perl compatible or
  • VIM syntax- using VIM

• About
  • most languages support regex matching
  • powerful way to do mass replacement, to replace inline ex. redacts a name, change all address formatting,

• SAMPLE SET
  • apple pear lemon orange

• USING REGEX COMMAND CHARACTERS + examples
  • ^ this is the beginning of a line
  • ex. ^l match for first letter is l

• $ match for the end of a string ex. e$ matches apple orange

• [ ] set inside the brackets - note that putting concurrent characters means any one of these characters
  • ex. [er]$ matches apple pear
  • ex. [a-e]$ matches
  • ex. york matches only "york" but [york] matches y, o, r, or k

• + one or more charachters
  • ex. [aer]+$ apple pear orange

• 0 or more charachters - note that all strings are returned using this b/c of including "0" instances
  • ex. [aer]*$ apple pear lemon orange

• {} uses a number to match the command ex [a-z]{2,3}$ matches the last 2 or 3 characters within the defined set to seach
• w/i, in this case a-z

• \ escapes single character of what comes directly after

• \w escapes w and runs command to looks for words

• ! negative, ensure this does not appear

EXAMPLES

• set: nick_newyork betty_texas anne_houston buffalo [a-z0-9_]$
  • ^[a-z]+$ just selects the names
  • ^[a-z_]+$ selects all, includes _ to continue along the string searched
  • [a-z ]+$ note the space, selects nothing, looking at the end
  • ^[a-z ] note the space, selects everything, looking from the beginning

MORE USE -- SEARCH AND REPLACE

• Look Behind and Look Ahead
• ?<= ?>=
• Using the side carats to point the search functions

• () parens are for groups of charachters, of multiple charchters note [] brackets are for sets
  • ex. ([A-Z]{2})_([A-Z ])+$ again, note space in second group rertuns nick_new york anne_houston

• ? this might not appear
  • ([A-Z])?_([A-Z ])+$ says you might not see this groupg

MORE USE EXAMPLES

• 1. Pick out email addresses in a document
• [\w.] - any word including any .
• [\w.]+@([a-z-]+.)+[a-z]{2-4}
  • any word of 1 or more characters, then @, then a set that may occur multiply,
• then the TLD
  • [\w.+]+@([a-z-]+.)+[a-z]{2-4}
  • here we added a + in the set to instruct that it is a searchable character, to include

                       testing+myemail.com
               
               

USE NOTES

• case matters [a or A]
• alot of regex is fighting with regex, it can be frustration
• try expressing the logic of what you're searching for ahead of time -- can help you formulate

DELIMITERS

• /i placed at the end means case insensitive

• REFERENCE URLs

• Regexper.com -- demonstrates logic of a regex
• Regular-Expressions.info
• Rubular - Ruby regex

• Command line tools
  • - sed [replace] ex. echo "hello there" | sed "s/hello/whatsup/g"-> whatsup there ex. - egrep [search] or grep -e [extended regexp] ex. egrep '^a' /file/path - returns anything that starts with a

VIM

• Will need to escape characters in the command program itself \ use your escape characters
  • ex. ^[aeiou]\+$
  • look for words that start w a vowel with one or more characters matching a vowel at the end
  • ex. Do this
  • ex. Returning Odd numbers: [0-9]+?[13579] same as [[0-9]*[13579]- you'll see 0-9 0 or more times, then after 1, 3, 5, 7, or 9 after.