Regular Expressions & grep

Regular Expressions

Pattern	Matches
`.`	Any single character
`*`	Zero or more of the previous
`^`	Start of line
`$`	End of line
`[abc]`	Any one of a, b, c
`[^abc]`	Any character except a, b, c
`\{2,4\}`	2 to 4 repetitions (BRE)
`\	`	Alternation (BRE)

grep flags: -i ignore case, -v invert, -r recursive, -n line numbers, -c count, -E extended regex, -o only matching part, -w whole word.

$ grep -E '^[0-9]{3}-[0-9]{4}
  

 contacts.txt   # phone numbers
$ grep -rn 'TODO' src/

Exam tip: BRE (basic) requires \{ \} and \|; ERE (extended, grep -E) uses bare { } and |. egrep = grep -E.