Regex

General

• xxx

Characters

• ^
  • beginning of the line
• $
  • end of line
• .
  • any single character
• [ ]
  • range of characters
• to use any of these special characters as normal characters, preface them with a \.
  • \$

Special match patterns

• [:alnum:] => alphanumeric character
• [:alpha:] => letters
• [:asccii:] => ascii characters
• [:blank:] => space or tab
• [:cntrl:] => ascii control characters
• [:digit:] => digits
• [:graph:] => noncontrol, nonspace characters
• [:lower:] => lowercase
• [:print:] => printable characters
• [:punct:] => punctuation characters
• [:space:] => whitespace characters, including vertical tab
• [:upper:] => uppercase
• [:xdigit:] => hex digits

Extended regex characters

• ?
  • match is optional, but may be matched once at most
• *
  • must be matched zero or more times
• +
  • must be matched one or more times
• {n}
  • must be matched n times
• {n,}
  • must be matched n or more times
• {n,m}
  • must be matched between n or m times inclusive

Examples

• grep e$ blah.txt
  • find words that end in e in the file blah.txt
• grep ablank: blah.txt
  • find words that end with the letter a. blank checks for a space or tab after a
• grep Th.space: blah.txt
  • find three letter words that start with Th
• grep -E [a-z]\{10\} blah.txt
  • Extended grep that searches for lowercase words that are exactly 10 characters long
  • I guess the curlies need to be escaped