Regular Expression

2019-10-01 1 minute read

Character Classes[0123456789]. It matches any single character in that list.
- [^0123] any character not in the list.
- [a-d] equivalent to [abcd].
- Predefined expressions, [:alnum:], [:alpha:], [:digit:], [:lower:], [:punct:], [:space:], [:upper:]
Special Expressions
- . any single character
- \s any white space (spaces, tab and new line), \S any non white space
- \d any digits, \D any non-digits
- \w any word characters (letters, digits and underscore), any non-word
Anchoring
- ^exp a line begin with exp.
- exp$ a line end with exp.
- \<exp a word begin with exp.
- exp\> a word end with exp. \<c...h\>
Repetition
- a? The preceding item is optional and matched at most once.
- a* The preceding item will be matched zero or more times.
- a+ The preceding item will be matched one or more times.
- a{n} The preceding item is matched exactly n times.
- a{n,m} The preceding item is matched at least n and at most m times.
Back References and Sub-expressions
- (exp) enclosed in parentheses may be referred to later in the expression.
- \1 the substring previously matched by the 1st parenthesized sub-expression
Alternation
- (a|b) a or b

Example

find two lines with the same precedent and different suffixes.

([\w-]).cc[│\s]\1.h