egrep: the extended global regular expression print in Unix allows to search for a string or complex patterns in a file. Regular expressions provide a convenient, compact way of expressing patterns.

Regular expressions in egrep are written slightly dofferently. For example, Kleen closure operator(^*) is written as * (not superscript), union (È) is denoted by verticle bar (\mid). Parentheses have their usual meaning as grouping operators. The alphabet (å) is denoted by a period (.), i.e., matches any character.

For example, the regular expression (abÈc)^* would be denoted as (ab \mid c)*, and å^* would be denoted as .*

There is no way to express the empty string in egrep. Instead, r? denotes zero or more occurences of the regular expression r, so the empty string is not needed in practice.

Special characters beginning of line is denoted by ^
and end of line is denoted by $

Expression	egrep notation
r*	r*
r+	r+
r Èl	r?
r Ès	r\mid s
rs	rs
(r)	(r)
å	.

• The command

  %egrep  'depend' /usr/dict/words
  

  searches the dictionary for all words containing depend as substring.

• To find words of two or more letters that begin and end with y, we could type

  %egrep '^y.*y$' /usr/dict/words
  

  In contrast, the command

  %egrep 'y.*y' /usr/dict/words
  

  results in a list of 113 words

• For help with spelling we might type

  %egrep '^rec(ei|ie)ve$' /usr/dict/words
  

• For help with crossword puzzle we might type

  %egrep '^s..u.t..e$' /usr/dict/words