POSIX RegEx

posix

# Info 'man 7 regex'

POSIX Basic Regular Expressions (BRE)
+ - ordinary char
? - ordinary char
| - ordinary char
\{\} - special chars
{} - regular chars
\(\) - special
() - regular

       Obsolete  ("basic") regular expressions differ in several respects.  '|', '+', and '?' are ordinary characters and there is no equivalent for their functionality.  The delimiters for bounds are "\{"
       and "\}", with '{' and '}' by themselves ordinary characters.  The parentheses for nested subexpressions are "\(" and "\)", with '(' and ')' by themselves ordinary characters.  '^'  is  an  ordinary
       character except at the beginning of the RE or(!) the beginning of a parenthesized subexpression, '$' is an ordinary character except at the end of the RE or(!) the end of a parenthesized subexpres-
       sion, and '*' is an ordinary character if it appears at the beginning of the RE or the beginning of a parenthesized subexpression (after a possible leading '^').


POSIX Extended Regular Expressions (ERE)

Special characters
* - 0 or more times 
+ - 1 ore more times
? - 0 or 1 time
. - any char
| - alternating match
{1} - one time 
{1,2} - one ore two times
{1,} - at least one time
(grouping) - grouping expressions
[] - character class
       A  bracket expression is a list of characters enclosed in "[]".  It normally matches any single character from the list (but see below).  If the list begins with '^', it matches any single character
       (but see below) not from the rest of the list.  If two characters in the list are separated by '-', this is shorthand for the full range of characters between those two (inclusive) in the  collating
       sequence,  for  example,  "[0-9]"  in ASCII matches any decimal digit.  It is illegal(!) for two ranges to share an endpoint, for example, "a-c-e".  Ranges are very collating-sequence-dependent, and
       portable programs should avoid relying on them.

\ - escape character
^ - start of the line
$ - end of the line

       Within a bracket expression, the name of a character class enclosed in "[:" and ":]" stands for the list of all characters belonging to that class.  Standard character class names are:

              alnum   digit   punct
              alpha   graph   space
              blank   lower   upper
              cntrl   print   xdigit