Regular expressions (RE)

basic       BRE

extended ERE

Atoms

        (re)  matches a match for re (re is any regular expression) with  the

               match noted for possible reporting

         [chars]

               a bracket expression,  matching  any  one  of  the  chars

         .     matches any single character

         \k    matches  the  non-alphanumeric character k taken as an ordinary

               character, e.g. \\ matches a backslash character

         \c    where c is alphanumeric (possibly  followed  by  other  charac-

               ters), an escape (AREs only),

         {     when  followed  by  a character other than a digit, matches the

               left-brace character “{”; when followed by a digit, it  is  the

               beginning of a bound

         x     where  x  is  a  single  character  with no other significance,

               matches that character.

Bracket

       [0123456789]    any of the characters

       [0-9a-zA-Z]        any characters in the range

       [^0-9a-zA-Z]     negation

Character classes

       [:name:]

       alpha   A letter.

       upper   An upper-case letter.

       lower   A lower-case letter.

       digit   A decimal digit.

       xdigit  A hexadecimal digit.

       alnum   An alphanumeric (letter or digit).

       print   A "printable" (same as graph, except also including space).

       blank   A space or tab character.

       space   A character producing white space in displayed text.

       punct   A punctuation character.

       graph   A character with a visible representation (includes both  alnum

               and punct).

       cntrl   A control character.

Escape characters

         \a   alert (bell) character, as in C

         \b   backspace, as in C

         \f   formfeed, as in C

         \n   newline, as in C

         \r   carriage return, as in C

         \t   horizontal tab, as in C

         \v   vertical tab, as in C are all available.

         \0   the character whose value is 0

Class-escapes

         \d        [[:digit:]]

         \s        [[:space:]]

         \w        [[:alnum:]_]

         \D        [^[:digit:]]

         \S        [^[:space:]]

         \W        [^[:alnum:]_]

Quantifyers

        *     a sequence of 0 or more matches of the atom

         +     a sequence of 1 or more matches of the atom

         ?     a sequence of 0 or 1 matches of the atom

         {m}   a sequence of exactly m matches of the atom

         {m,}  a sequence of m or more matches of the atom

         {m,n} a  sequence  of  m through n (inclusive) matches of the atom; m may not exceed n

         *?  +?  ??  {m}?  {m,}?  {m,n}?   non-greedy

Anchors

         ^       matches at the beginning of a line

         $       matches at the end of a line